全文获取类型
收费全文 | 1806篇 |
免费 | 123篇 |
国内免费 | 1篇 |
专业分类
1930篇 |
出版年
2023年 | 10篇 |
2022年 | 25篇 |
2021年 | 48篇 |
2020年 | 41篇 |
2019年 | 49篇 |
2018年 | 65篇 |
2017年 | 33篇 |
2016年 | 79篇 |
2015年 | 102篇 |
2014年 | 101篇 |
2013年 | 117篇 |
2012年 | 145篇 |
2011年 | 140篇 |
2010年 | 73篇 |
2009年 | 108篇 |
2008年 | 92篇 |
2007年 | 101篇 |
2006年 | 104篇 |
2005年 | 72篇 |
2004年 | 70篇 |
2003年 | 53篇 |
2002年 | 36篇 |
2001年 | 38篇 |
2000年 | 22篇 |
1999年 | 30篇 |
1998年 | 16篇 |
1997年 | 12篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1974年 | 5篇 |
1971年 | 3篇 |
1970年 | 4篇 |
1969年 | 2篇 |
1968年 | 3篇 |
1965年 | 1篇 |
排序方式: 共有1930条查询结果,搜索用时 0 毫秒
1.
Rosalem Gabriel Santos Las Casas Estevam Barbosa Lima Thiago Parente González-Torres Libardo Andrés 《Biomechanics and modeling in mechanobiology》2020,19(5):1537-1549
Biomechanics and Modeling in Mechanobiology - Cell migration is a process of crucial importance for the human body. It is responsible for important processes such as wound healing and tumor... 相似文献
2.
Late Quaternary climate change,relict populations and present‐day refugia in the northern Atacama Desert: a case study from Quebrada La Higuera (18° S) 下载免费PDF全文
3.
Philippe Fernandez‐Fournier Samantha Straus Ruth Sharpe Leticia Avils 《Ecological Entomology》2019,44(2):157-162
1. Manipulation of host behaviour by parasitoids has long captured the imagination of ecologists. Parasitoid wasps in the Polysphincta group of genera develop as external parasitoids of spiders. 2. In the present study, the previously undescribed interaction between a Zatypota sp. wasp (Ichneumonidae) and a social spider Anelosimus eximius (Theridiidae) is described. The larva of this Zatypota wasp is found to induce its host to disperse from their communal web and build an entirely enclosed web consisting of densely spun silk. 3. The wasp is observed to target primarily immature A. eximius individuals, with 37.5–44% of nests in a given area being parasitised. Of those nests, approximately 1.3–2.0% of individuals are hosts to the parasitoid larvae. Larger spider colonies had a significantly higher probability of harbouring parasitoids. 4. This interaction results in unusual behaviours for A. eximius induced by the parasitoid: (i) leaving the protection of the social nest and (ii) building a unique, altered web that it would not otherwise build. It is suggested that the wasp may be tapping into ancestral dispersal behaviours in its host and that a social species provides this wasp an evolutionary advantage by allowing a stable host source. 相似文献
4.
Ricardo Godoy Christopher P. A. Bennett 《Human ecology: an interdisciplinary journal》1991,19(1):83-98
This article contains a comparison of the profits of cultivating modern and traditional varieties of coconuts as a monocrop and as an intercrop, in ideal and in average growing conditions, with good and with average management. We carry out the analysis from a private (financial) and from a national (economic) perspective. The results show that intercropping generates more income than monocropping. In the conclusion we discuss why development organizations and Third World countries encourage monocropping. 相似文献
5.
Abstract. 1. Most of what is known about parasitoid behaviour comes from laboratory observations: field quantitative observations on searching parasitoids are extremely difficult to do and are rare. The basic components of Aphytis melinus 's response to California red scale ( Aonidiella aurantii ) were studied in the laboratory: encounter, rejection, drumming, probing, oviposition, and host-feeding. It was then asked whether these observations provided a reliable guide to behaviour in the field in a situation that was very different from the laboratory.
2. Field observations were carried out on bark on the trunk and interior branches of trees where live scale density is extremely high in patches, dead scale make up 90% of all scale, and could be expected to interfere with Aphytis search.
3. The laboratory observations predicted well the time taken in the field for each basic event (drumming or probing) and average times spent on a scale. Also well predicted were the distributions of times spent on drumming, probing, and total time on a scale. Rejection rates were much higher in the field. Thus, the laboratory studies predicted foraging behaviour in the field with variable success; potential explanations for observed mismatch between laboratory and field and its possible larger implications are discussed. 相似文献
2. Field observations were carried out on bark on the trunk and interior branches of trees where live scale density is extremely high in patches, dead scale make up 90% of all scale, and could be expected to interfere with Aphytis search.
3. The laboratory observations predicted well the time taken in the field for each basic event (drumming or probing) and average times spent on a scale. Also well predicted were the distributions of times spent on drumming, probing, and total time on a scale. Rejection rates were much higher in the field. Thus, the laboratory studies predicted foraging behaviour in the field with variable success; potential explanations for observed mismatch between laboratory and field and its possible larger implications are discussed. 相似文献
6.
Francesc Gòdia Carles Casas Bernardo Castellano Carles Solà 《Applied microbiology and biotechnology》1987,26(4):342-346
Summary Data of cell concentration, viability and microscopic observation of cell distribution inside carrageenan immobilized yeast beads are reported. Results were obtained from a continuous packed-bed reactor performing alcoholic fermentation and the main observations made on cell activity are in agreement with the fermentation profiles inside the fermenter. 相似文献
7.
Immediate breast reconstruction: reducing the risks 总被引:2,自引:0,他引:2
M H Bailey J W Smith L Casas P Johnson E Serra R de la Fuente M Sullivan E F Scanlon 《Plastic and reconstructive surgery》1989,83(5):845-851
One-hundred and sixty-five consecutive immediate breast reconstructions in 157 patients were reviewed. Reconstructions were performed with tissue expanders (53 percent) or immediate gel prostheses (47 percent). Immediate reconstruction was associated with an 18 percent rate of implant loss. Certain risk factors were identified at the p less than 0.05 level using immediate gel implants: failure to achieve complete muscle coverage of the implant, smoking at the time of surgery, initial gel implants of 400 ml or more volume, and age. Expander loss was increased by detaching the pectoralis major (p less than 0.05) and probably by lack of complete muscle coverage in general. Chemotherapy, history of previous smoking, and clinical stage of the carcinoma did not seem to affect reconstructive success. Smoking and patient age should be considered during patient selection for immediate reconstruction. Muscle coverage of the prosthesis should always be attempted. Muscle coverage is mandatory in the smoker. Gel implants of 400 ml or more volume are to be avoided at the initial operation. This approach should enable all surgeons to achieve lower rates of implant loss. 相似文献
8.
Summary The influence of starvation on renal carbohydrate metabolism was studied in the proximal and distal fragments of the nephron. Starvation induced a double and opposite adaptation mechanism in both fractions of the renal tubule. In renal proximal tubules, the gluconeogenic flux was stimulated progressively during a period of 48 hours of starvation (2.15 fold), due, in part, to a significant increase in the fructose 1,6-bisphosphatase and phosphoenolpyruvate carboxykinase activities although with different characteristics. Fructose 1,6-bisphosphatase activity from this tubular fragment increased only at subsaturating subtrate concentration (68%) which involved a significant decrease in the Km (35%) for fructose 1,6-bisphosphate while there was no change in Vmax. This behaviour clearly indicates that it is related to modifications in the activity of the preexistent enzyme in the cell. Proximal phosphoenolpyruvate carboxykinase activity increased proportionally at both substrate concentrations (86 and 89% respectively) which brought about changes in Vmax without changes in Kin, all of which are in accordance with variations in the cellular levels of the enzyme. In the renal distal tubules, the glycolytic capacity drastically decreased throughout the starvation time. At 48 hours 65% of inhibition was shown. We have found a short term regulation of phosphofructokinase activity by starvation which involves an increase in Km (2.2 fold) without changes in Vmax, as a result of these kinetic changes, an inactivation of phosphofructokinase was detected at subsaturating concentration of fructose 6-phosphate. On the contrary, this nutritional state did not modify the kinetic behaviour of renal pyruvate kinase. Finally, neither proximal glycolytic nor distal gluconeogenic capacities and related enzymes activities were changed during starvation. 相似文献
9.
Pathology of the human pulmonary paracoccidioidomycosis 总被引:1,自引:1,他引:0
Lungs of twelve patients with chronic paracoccidioidomycosis (Pb) were studied in an attempt to understand the pathogenesis of the pulmonary disease. Ribbons of the lung parenchyma including the hilar region and directed towards apical, basal and lateral regions were subdivided into sections from the hilar, intermediate and peripheral segments. The following histopathological reactions directly or indirectly related to P. brasiliensis were described and analysed in relation to the number of slides studied and the pulmonary region involved: (1) pneumonic reaction; (2) early granulomatous formation; (3) mature and healed granulomata; (4) mixed pattern (early and mature granuloma in the same pulmonary area visualized in the slide); (5) pulmonary fibrosis.It was concluded that chronic pulmonary Pb is a recurrent disease affecting equally both lungs. Fibrosis was connected mainly with the progressive evolution of the granulomata towards cicatrization and to a lesser degree probably to a direct induction by the fungi. Based chiefly on the tendency of the fibrosis to run around bronchi and to make up septa interconnecting bronchi and vessels it was hipothesized that these findings were the result of a previous chronic specific lymphangitis by the fungi. Hilar fibrosis would be the result of this lymphangitis and/or of the progression of the specific granulomatous reaction seen in the hilar lymph nodes.Non specific forms of arteritis and areas of destructive emphysema related to granulomatous inflammation and fibrosis were described. Three cases developed pulmonary hypertension. 相似文献
10.
A tomato cDNA inducible by salt stress and abscisic acid: nucleotide sequence and expression pattern 总被引:2,自引:0,他引:2
We have characterized a new tomato cDNA, TAS14, inducible by salt stress and abscisic acid (ABA). Its nucleotide sequence predicts an open reading frame coding for a highly hydrophilic and glycine-rich (23.8%) protein of 130 amino acids. Southern blot analysis of tomato DNA suggests that there is one TAS14 structural gene per haploid genome. TAS14 mRNA accumulates in tomato seedlings upon treatment with NaCl, ABA or mannitol. It is also induced in roots, stems and leaves of hydroponically grown tomato plants treated with NaCl or ABA. TAS14 mRNA is not induced by other stress conditions such as cold and wounding. The sequence of the predicted TAS14 protein shows four structural domains similar to the rice RAB21, cotton LEA D11 and barley and maize dehydrin genes. 相似文献