全文获取类型
收费全文 | 574篇 |
免费 | 33篇 |
国内免费 | 5篇 |
出版年
2022年 | 1篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2017年 | 10篇 |
2016年 | 1篇 |
2015年 | 5篇 |
2014年 | 18篇 |
2013年 | 162篇 |
2012年 | 59篇 |
2011年 | 26篇 |
2010年 | 17篇 |
2009年 | 19篇 |
2008年 | 16篇 |
2007年 | 9篇 |
2006年 | 12篇 |
2005年 | 8篇 |
2004年 | 9篇 |
2003年 | 5篇 |
2002年 | 13篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 11篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 8篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 17篇 |
1983年 | 18篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有612条查询结果,搜索用时 15 毫秒
1.
《Saudi Journal of Biological Sciences》2017,24(1):226-233
Morphological, anatomical and physiological plasticity was examined for Cakile arabica from three different sites at the coastal part of the Arabian Gulf near Ad Dammam city in the eastern region of Saudi Arabia. Morphological investigation showed that the size and number of lobes of the leaves are increased in sites (I) which have high salt stress. Also anatomical investigation using a light microscope showed that the plant is adaptive for salt stress by increasing the thickening of the cuticle or epidermis layer and increase in the area of vascular bundles. Physiological studies showed that plant growing under high salt stress is characterized by increase content of electrical conductivity and increase in chlorophyll a, b, carotenoids and proline content in the plant tissues. This can be explained as an osmotic adjustment mechanism for the investigated species growing under high salinity stress. 相似文献
2.
Grace Fergusson Mélanie Ethier Bader Zarrouki Ghislaine Fontés Vincent Poitout 《Journal of visualized experiments : JoVE》2013,(78)
Chronic exposure to excessive levels of nutrients is postulated to affect the function of several organs and tissues and to contribute to the development of the many complications associated with obesity and the metabolic syndrome, including type 2 diabetes. To study the mechanisms by which excessive levels of glucose and fatty acids affect the pancreatic beta-cell and the secretion of insulin, we have established a chronic nutrient infusion model in the rat. The procedure consists of catheterizing the right jugular vein and left carotid artery under general anesthesia; allowing a 7-day recuperation period; connecting the catheters to the pumps using a swivel and counterweight system that enables the animal to move freely in the cage; and infusing glucose and/or Intralipid (a soybean oil emulsion which generates a mixture of approximately 80% unsaturated/20% saturated fatty acids when infused with heparin) for 72 hr. This model offers several advantages, including the possibility to finely modulate the target levels of circulating glucose and fatty acids; the option to co-infuse pharmacological compounds; and the relatively short time frame as opposed to dietary models. It can be used to examine the mechanisms of nutrient-induced dysfunction in a variety of organs and to test the effectiveness of drugs in this context. 相似文献
3.
Stroke is the third cause of mortality and the leading cause of disability in the World. Ischemic stroke accounts for approximately 80% of all strokes. However, the thrombolytic tissue plasminogen activator (tPA) is the only treatment of acute ischemic stroke that exists. This led researchers to develop several ischemic stroke models in a variety of species. Two major types of rodent models have been developed: models of global cerebral ischemia or focal cerebral ischemia. To mimic ischemic stroke in patients, in whom approximately 80% thrombotic or embolic strokes occur in the territory of the middle cerebral artery (MCA), the intraluminal middle cerebral artery occlusion (MCAO) model is quite relevant for stroke studies. This model was first developed in rats by Koizumi et al. in 1986 1. Because of the ease of genetic manipulation in mice, these models have also been developed in this species 2-3.Herein, we present the transient MCA occlusion procedure in C57/Bl6 mice. Previous studies have reported that physical properties of the occluder such as tip diameter, length, shape, and flexibility are critical for the reproducibility of the infarct volume 4. Herein, a commercial silicon coated monofilaments (Doccol Corporation) have been used. Another great advantage is that this monofilament reduces the risk to induce subarachnoid hemorrhages. Using the Zeiss stereo-microscope Stemi 2000, the silicon coated monofilament was introduced into the internal carotid artery (ICA) via a cut in the external carotid artery (ECA) until the monofilament occludes the base of the MCA. Blood flow was restored 1 hour later by removal of the monofilament to mimic the restoration of blood flow after lysis of a thromboembolic clot in humans. The extent of cerebral infarct may be evaluated first by a neurologic score and by the measurement of the infarct volume. Ischemic mice were thus analyzed for their neurologic score at different post-reperfusion times. To evaluate the infarct volume, staining with 2,3,5-triphenyltetrazolium chloride (TTC) was usually performed. Herein, we used cresyl violet staining since it offers the opportunity to test many critical markers by immunohistochemistry. In this video, we report the MCAO procedure; neurological scores and the evaluation of the infarct volume by cresyl violet staining. 相似文献
4.
Katherine J. Wert Jessica M. Skeie Richard J. Davis Stephen H. Tsang Vinit B. Mahajan 《Journal of visualized experiments : JoVE》2012,(69)
The loss of sight affects approximately 3.4 million people in the United States and is expected to increase in the upcoming years.1 Recently, gene therapy and stem cell transplantations have become key therapeutic tools for treating blindness resulting from retinal degenerative diseases. Several forms of autologous transplantation for age-related macular degeneration (AMD), such as iris pigment epithelial cell transplantation, have generated encouraging results, and human clinical trials have begun for other forms of gene and stem cell therapies.2 These include RPE65 gene replacement therapy in patients with Leber''s congenital amaurosis and an RPE cell transplantation using human embryonic stem (ES) cells in Stargardt''s disease.3-4 Now that there are gene therapy vectors and stem cells available for treating patients with retinal diseases, it is important to verify these potential therapies in animal models before applying them in human studies. The mouse has become an important scientific model for testing the therapeutic efficacy of gene therapy vectors and stem cell transplantation in the eye.5-8 In this video article, we present a technique to inject gene therapy vectors or stem cells into the subretinal space of the mouse eye while minimizing damage to the surrounding tissue. 相似文献
5.
Astrocytes form together with neurons tripartite synapses, where they integrate and modulate neuronal activity. Indeed, astrocytes sense neuronal inputs through activation of their ion channels and neurotransmitter receptors, and process information in part through activity-dependent release of gliotransmitters. Furthermore, astrocytes constitute the main uptake system for glutamate, contribute to potassium spatial buffering, as well as to GABA clearance. These cells therefore constantly monitor synaptic activity, and are thereby sensitive indicators for alterations in synaptically-released glutamate, GABA and extracellular potassium levels. Additionally, alterations in astroglial uptake activity or buffering capacity can have severe effects on neuronal functions, and might be overlooked when characterizing physiopathological situations or knockout mice. Dual recording of neuronal and astroglial activities is therefore an important method to study alterations in synaptic strength associated to concomitant changes in astroglial uptake and buffering capacities. Here we describe how to prepare hippocampal slices, how to identify stratum radiatum astrocytes, and how to record simultaneously neuronal and astroglial electrophysiological responses. Furthermore, we describe how to isolate pharmacologically the synaptically-evoked astroglial currents. 相似文献
6.
P.I.P. Perera V. Hocher L.K. Weerakoon D.M.D. Yakandawala S.C. Fernando J.-L. Verdeil 《South African Journal of Botany》2010
Palms are generally characterized by a large structure with a massive crown that creates difficulties in anatomical studies. The flowering behaviour of palm species may be a useful indicator of phylogenetic relationships and therefore evolutionary events. This paper presents a detailed histological study of reproductive development in coconut (Cocos nucifera L.), from initiation up to maturation of staminate and pistillate flowers. Reproductive development in coconut consists of a sequence of individual events that span more than two years. Floral morphogenesis is the longest event, taking about one year, while sex determination is a rapid process that occurs within one month. The inflorescence consists of different ultimate floral structural components. Pistillate flowers are borne in floral triads that are flanked by two functional staminate flowers. The staminate flowers are born in floral diads towards the base of the rachilla followed by solitary flowers in the middle to top of the rachilla. Three primary phases were identified in reproductive development, namely, transition of axillary bud into inflorescence bud, formation of floral buds, and sexualisation of individual flower buds. All developmental events with respect to stage or time of occurrence were determined. 相似文献
7.
Nuclei from Chinese hamster testicular cells in suspension were prepared in a sucrose gradient. Following the basic procedure of Blobel and co-workers for separating a fibrous lamina-nuclear pore complex, synaptonemal complexes (SCs) from spermatocytes were isolated free of other nuclear structures, except for fibrillar tufts at the attachment plaques in which annuli were observed. All the major morphological components of the SC appeared to be intact, showing that the structure could survive the procedure and was not dispersed by the removal of DNA with DNase and solubilization of membranes and some proteins with Triton X-100. Isolated sex bodies were also well preserved, as were various structures from other cell types in the mixed cell suspension, such as spermatid manchettes, acrosomal ‘ghosts’, axonemes, etc. While no nuclear matrix was found associated with autosomal SCs, a residual material was present in the sex body, in which the X and Y axes were embedded. The results indicate the feasibility of isolating and fractionating SCs from testicular cell suspensions enriched for pachytene spermatocytes. The association between SC attachment plaques and annuli that is seen in spreads of whole nuclei persists through the isolation procedure and implies an integrated structural relationship. 相似文献
8.
Inmaculada Moreno-Alías Lorenzo León Raúl de la Rosa Hava F. Rapoport 《Trees - Structure and Function》2009,23(1):181-187
The olive tree (Olea europaea L.), like many other woody plants, has a long juvenile period in which the plant is not able to produce flowers. Knowledge
of the moment when the plant is capable of flowering is important for breeding programs and also for determining the physiological
basis for sexual reproductive behavior, but currently the only indicator of that moment is the actual flowering. In many species,
the juvenile-to-adult phase shift includes changes in leaf structure known as heteroblasty, that is, varied form of successive
leaves on the same plant. Some differences have been observed between juvenile and adult olive leaves, particularly in size
and form, but to our knowledge, no complete systematic study has been carried out. In this research, we measured size, morphology
and anatomy for juvenile and adult leaves of olive plants grown from seeds. Differences were found in most of the parameters
studied, including leaf size, form, mesophyll thickness, layers of palisade parenchyma and quantity of peltate trichomes,
which were generally significant but overlapping between the two leaf types. The most consistent and striking difference was
the presence of an organized layer of subepidermal cells only in the abaxial mesophyll of adult leaves. This characteristic
could be a simple and effective criterion of phase change in the olive tree. 相似文献
9.
Summary The floral nectary ofPisum sativum L. is situated on the receptacle at the base of the gynoecium. The gland receives phloem alone which departed the vascular bundles supplying the staminal column. Throughout the nectary, only the companion cells of the phloem exhibited wall ingrowths typical of transfer cells. Modified stomata on the nectary surface served as exits for nectar, but stomatal pores developed well before the commencement of secretion. Furthermore, stomatal pores on the nectary usually closed by occlusion, not by guard-cell movements. Pore occlusion was detected most frequently in post-secretory and secretory glands, and less commonly in pre-secretory nectaries. A quantitative stereological study revealed few changes in nectary fine structure between buds, flowers secreting nectar, and post-secretory flowers. Dissolution of abundant starch grains in plastids of subepidermal secretory cells when secretion commenced suggests that starch is a precursor of nectar carbohydrate production. Throughout nectary development, mitochondria were consistently the most plentiful organelle in both epidermal and subepidermal cells, and in addition to the relative paucity of dictyosomes, endoplasmic reticulum, and their associated vesicles, the evidence suggests that floral nectar secretion inP. sativum is an energy-requiring (eccrine) process, rather that granulocrine.Abbreviations ER
endoplasmic reticulum
- GA
glutaraldehyde
- SEM
scanning electron microscopy 相似文献
10.
The genusPereskia, which contains numerous morphological features considered relictual in the Cactaceae, has numerous anatomical features that
we consider to be relictual also. These were studied to establish a basis for determining the ways that morphogenic mechanisms
and anatomical characters diversified as the family evolved. ThesePereskia features may be relictual in the family: epidermis predominantly unistratose and lacking crystals; hypodermis absent or of
about three layers of weakly collenchymatous cells with druses; cortex thin and predominantly parenchyma with druses and mucilage
cells but lacking cortical bundles; secondary phloem without early differentiation of sclerenchyma but with secondary sclereids
developing later, either idioblastically or in clusters; ergastic substances lacking from old secondary phloem; wood with
a matrix of libriform fibers (mostly septate and nucleate), scanty paratracheal parenchyma, vessels solitary or in small clusters,
perforations simple, pitting circular, oval or very broad; wide-band tracheids absent; ray cells slightly thick-walled, lignified,
upright, isodiametric or procumbent; all primary rays narrow; pith without medullary bundles; leaves lacking hypodermis, with
only weak development of palisade mesophyll; veins of four orders, strongly distinct in size, none with fibers; vessels in
leaves narrower than those in stems. 相似文献