全文获取类型
收费全文 | 2167篇 |
免费 | 106篇 |
国内免费 | 137篇 |
出版年
2023年 | 23篇 |
2022年 | 30篇 |
2021年 | 45篇 |
2020年 | 42篇 |
2019年 | 51篇 |
2018年 | 44篇 |
2017年 | 54篇 |
2016年 | 47篇 |
2015年 | 58篇 |
2014年 | 180篇 |
2013年 | 238篇 |
2012年 | 166篇 |
2011年 | 123篇 |
2010年 | 78篇 |
2009年 | 126篇 |
2008年 | 130篇 |
2007年 | 132篇 |
2006年 | 90篇 |
2005年 | 67篇 |
2004年 | 58篇 |
2003年 | 62篇 |
2002年 | 51篇 |
2001年 | 46篇 |
2000年 | 27篇 |
1999年 | 36篇 |
1998年 | 37篇 |
1997年 | 34篇 |
1996年 | 40篇 |
1995年 | 28篇 |
1994年 | 30篇 |
1993年 | 27篇 |
1992年 | 22篇 |
1991年 | 24篇 |
1990年 | 22篇 |
1989年 | 15篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 3篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1971年 | 5篇 |
排序方式: 共有2410条查询结果,搜索用时 218 毫秒
71.
72.
开展生态系统服务评估已经成为国土空间功能管治、城市治理、生态产品价值实现等工作中的先行基础动作。生态系统服务的类型和模型方法多,数据需求复杂,传统基于多学科软件开展生态系统服务评估的工作模式知识和技术门槛较高、效率低。当前专业的生态系统服务评估软件多为美国从业人员开发,对我国的数据构成和本地化参数适应性有限。介绍了我国自主开发的生态系统分析软件(城市生态智慧管理系统,IUEMS)的主要功能和应用情况,并将其的生态系统服务评估功能与InVEST、ARIES等国外主流软件在操作逻辑、评估模型、数据取得、空间精度、界面交互五个方面进行了对比。 相似文献
73.
Lower screening uptake could impact cancer survival in rural areas. This systematic review sought studies comparing rural/urban uptake of colorectal, cervical and breast cancer screening in high income countries. Relevant studies (n = 50) were identified systematically by searching Medline, EMBASE and CINAHL. Narrative synthesis found that screening uptake for all three cancers was generally lower in rural areas. In meta-analysis, colorectal cancer screening uptake (OR 0.66, 95 % CI = 0.50−0.87, I2 = 85 %) was significantly lower for rural dwellers than their urban counterparts. The meta-analysis found no relationship between uptake of breast cancer screening and rural versus urban residency (OR 0.93, 95 % CI = 0.80–1.09, I2 = 86 %). However, it is important to note the limitation of the significant statistical heterogeneity found which demonstrates the lack of consistency between the few studies eligible for inclusion in the meta-analyses. Cancer screening uptake is apparently lower for rural dwellers which may contribute to poorer survival. National screening programmes should consider geography in planning. 相似文献
74.
Abstract The IUCN Red Lists assessment provides an internationally accepted system to verify the extinction risk of species. Working Groups of the Italian Botanical Society have recently discussed the importance of producing a reliable list of species at the national level. This list could be the starting point for future in situ and ex situ plant conservation activities. 相似文献
75.
Sophie Bouvard Patrice Faure Corinne Roucard Alain Favier Serge Halimi 《Free radical research》2013,47(9):1017-1022
HeLa cell line stably transfected with the tat gene from human immunodeficiency virus type 1 has a decreased antioxidant potential. In this work, we used this model to investigate the effect of a high glucose level (20 mM) on the glucose induced cytotoxicity and on the antioxidant system. In comparison to cell culture under control medium, HeLa-wild cell cultured under 20 mM glucose did not exhibit necrosis or apoptosis, contrary to HeLa-tat cell presenting a significant increase in necrotic or apoptotic state. Moreover after 48 h culture under high glucose level the HeLa-tat proliferation rate was not higher than the one of HeLa-wild cells. In HeLa-wild cell high glucose level resulted in an induction of glutathione reductase activity in opposition to HeLa-tat cells where no change was observed. High glucose level resulted in 20% increase in GSSG/GSH ratio in HeLa-wild cells and 38% increase in HeLa-tat cells. Moreover, high glucose level resulted in a dramatic cytosolic thiol decrease and an important lipid peroxidation in HeLa-tat cells. No significant change of these two parameters was observed in HeLa-wild cells. In both cell lines, high glucose resulted in an increase of total SOD activity, as a consequence of the increase in Cu,Zn-SOD activity. High glucose did not result in an increase of Mn-SOD activity in both cell lines. As a consequence of tat tranfection Mn-SOD activity was 50% lower in HeLa-tat cells in comparison to HeLa-wild cells. This work emphasizes the importance of the antioxidant system in the glucose induced cytotoxicity. 相似文献
76.
Andrew J. Woolley Himanshi A. Desai Janak Gaire Andrew L. Ready Kevin J. Otto 《Journal of visualized experiments : JoVE》2013,(72)
Research into the design and utilization of brain-implanted microdevices, such as microelectrode arrays, aims to produce clinically relevant devices that interface chronically with surrounding brain tissue. Tissue surrounding these implants is thought to react to the presence of the devices over time, which includes the formation of an insulating "glial scar" around the devices. However, histological analysis of these tissue changes is typically performed after explanting the device, in a process that can disrupt the morphology of the tissue of interest.Here we demonstrate a protocol in which cortical-implanted devices are collected intact in surrounding rodent brain tissue. We describe how, once perfused with fixative, brains are removed and sliced in such a way as to avoid explanting devices. We outline fluorescent antibody labeling and optical clearing methods useful for producing an informative, yet thick tissue section. Finally, we demonstrate the mounting and imaging of these tissue sections in order to investigate the biological interface around brain-implanted devices. 相似文献
77.
Kathrin Schüller Dominik Bühler Nikolaus Plesnila 《Journal of visualized experiments : JoVE》2013,(81)
In this video publication a standardized mouse model of subarachnoid hemorrhage (SAH) is presented. Bleeding is induced by endovascular Circle of Willis perforation (CWp) and proven by intracranial pressure (ICP) monitoring. Thereby a homogenous blood distribution in subarachnoid spaces surrounding the arterial circulation and cerebellar fissures is achieved. Animal physiology is maintained by intubation, mechanical ventilation, and continuous on-line monitoring of various physiological and cardiovascular parameters: body temperature, systemic blood pressure, heart rate, and hemoglobin saturation. Thereby the cerebral perfusion pressure can be tightly monitored resulting in a less variable volume of extravasated blood. This allows a better standardization of endovascular filament perforation in mice and makes the whole model highly reproducible. Thus it is readily available for pharmacological and pathophysiological studies in wild type and genetically altered mice. 相似文献
78.
Tricia H. Smith Joy Ngwainmbi John R. Grider William L. Dewey Hamid I. Akbarali 《Journal of visualized experiments : JoVE》2013,(78)
The enteric nervous system is a vast network of neurons and glia running the length of the gastrointestinal tract that functionally controls gastrointestinal motility. A procedure for the isolation and culture of a mixed population of neurons and glia from the myenteric plexus is described. The primary cultures can be maintained for over 7 days, with connections developing among the neurons and glia. The longitudinal muscle strip with the attached myenteric plexus is stripped from the underlying circular muscle of the mouse ileum or colon and subjected to enzymatic digestion. In sterile conditions, the isolated neuronal and glia population are preserved within the pellet following centrifugation and plated on coverslips. Within 24-48 hr, neurite outgrowth occurs and neurons can be identified by pan-neuronal markers. After two days in culture, isolated neurons fire action potentials as observed by patch clamp studies. Furthermore, enteric glia can also be identified by GFAP staining. A network of neurons and glia in close apposition forms within 5 - 7 days. Enteric neurons can be individually and directly studied using methods such as immunohistochemistry, electrophysiology, calcium imaging, and single-cell PCR. Furthermore, this procedure can be performed in genetically modified animals. This methodology is simple to perform and inexpensive. Overall, this protocol exposes the components of the enteric nervous system in an easily manipulated manner so that we may better discover the functionality of the ENS in normal and disease states. 相似文献
79.
Kota Yamamoto Xin Li Chang Shu Tetsuro Miyata Alan Dardik 《Journal of visualized experiments : JoVE》2013,(77)
Technical aspects of creating an arteriovenous fistula in the mouse are discussed. Under general anesthesia, an abdominal incision is made, and the aorta and inferior vena cava (IVC) are exposed. The proximal infrarenal aorta and the distal aorta are dissected for clamp placement and needle puncture, respectively. Special attention is paid to avoid dissection between the aorta and the IVC. After clamping the aorta, a 25 G needle is used to puncture both walls of the aorta into the IVC. The surrounding connective tissue is used for hemostatic compression. Successful creation of the AVF will show pulsatile arterial blood flow in the IVC. Further confirmation of successful AVF can be achieved by post-operative Doppler ultrasound. 相似文献
80.
One of the fundamental interests in neuroscience is to understand the integration of excitatory and inhibitory inputs along the very complex structure of the dendritic tree, which eventually leads to neuronal output of action potentials at the axon. The influence of diverse spatial and temporal parameters of specific synaptic input on neuronal output is currently under investigation, e.g. the distance-dependent attenuation of dendritic inputs, the location-dependent interaction of spatially segregated inputs, the influence of GABAergig inhibition on excitatory integration, linear and non-linear integration modes, and many more.With fast micro-iontophoresis of glutamate and GABA it is possible to precisely investigate the spatial and temporal integration of glutamatergic excitation and GABAergic inhibition. Critical technical requirements are either a triggered fluorescent lamp, light-emitting diode (LED), or a two-photon scanning microscope to visualize dendritic branches without introducing significant photo-damage of the tissue. Furthermore, it is very important to have a micro-iontophoresis amplifier that allows for fast capacitance compensation of high resistance pipettes. Another crucial point is that no transmitter is involuntarily released by the pipette during the experiment.Once established, this technique will give reliable and reproducible signals with a high neurotransmitter and location specificity. Compared to glutamate and GABA uncaging, fast iontophoresis allows using both transmitters at the same time but at very distant locations without limitation to the field of view. There are also advantages compared to focal electrical stimulation of axons: with micro-iontophoresis the location of the input site is definitely known and it is sure that only the neurotransmitter of interest is released. However it has to be considered that with micro-iontophoresis only the postsynapse is activated and presynaptic aspects of neurotransmitter release are not resolved. In this article we demonstrate how to set up micro-iontophoresis in brain slice experiments. 相似文献