全文获取类型
收费全文 | 193843篇 |
免费 | 6862篇 |
国内免费 | 895篇 |
专业分类
201600篇 |
出版年
2022年 | 781篇 |
2021年 | 1564篇 |
2020年 | 1286篇 |
2019年 | 1451篇 |
2018年 | 13724篇 |
2017年 | 12368篇 |
2016年 | 10302篇 |
2015年 | 4871篇 |
2014年 | 4841篇 |
2013年 | 6213篇 |
2012年 | 10845篇 |
2011年 | 18329篇 |
2010年 | 15483篇 |
2009年 | 11191篇 |
2008年 | 14300篇 |
2007年 | 15632篇 |
2006年 | 4894篇 |
2005年 | 4475篇 |
2004年 | 4956篇 |
2003年 | 4532篇 |
2002年 | 4061篇 |
2001年 | 2965篇 |
2000年 | 2663篇 |
1999年 | 2079篇 |
1998年 | 1027篇 |
1997年 | 781篇 |
1996年 | 782篇 |
1995年 | 719篇 |
1994年 | 663篇 |
1993年 | 613篇 |
1992年 | 1259篇 |
1991年 | 1198篇 |
1990年 | 1112篇 |
1989年 | 1176篇 |
1988年 | 990篇 |
1987年 | 1008篇 |
1986年 | 905篇 |
1985年 | 955篇 |
1984年 | 792篇 |
1983年 | 718篇 |
1979年 | 796篇 |
1978年 | 600篇 |
1975年 | 701篇 |
1974年 | 753篇 |
1973年 | 714篇 |
1972年 | 900篇 |
1971年 | 850篇 |
1970年 | 626篇 |
1969年 | 687篇 |
1968年 | 646篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Background
Radial chromosome positioning in interphase nuclei is nonrandom and can alter according to developmental, differentiation, proliferation, or disease status. However, it is not yet clear when and how chromosome repositioning is elicited. 相似文献102.
Background
In heterogeneous environments, sex-biased dispersal could lead to environmental adaptive parental effects, with offspring selected to perform in the same way as the parent dispersing least, because this parent is more likely to be locally adapted. We investigate this hypothesis by simulating varying levels of sex-biased dispersal in a patchy environment. The relative advantage of a strategy involving pure maternal (or paternal) inheritance is then compared with a strategy involving classical biparental inheritance in plants and in animals. 相似文献103.
H. Štorchová 《Biologia Plantarum》1994,36(3):358-358
104.
TNF inhibitors are currently considered both effective and cost-effective in patients with active rheumatoid arthritis (RA),
particularly in patients who have not responded fully to methotrexate. There is substantial doubt about the cost-effectiveness
of TNF inhibitors as initial treatment for active RA. New data from the National Data Bank for Rheumatic Diseases now question
the current consensus in methotrexate failures. The data suggest that in routine clinical practice TNF inhibitors provide
only modest incremental benefits over best conventional therapy. If confirmed, these observational studies suggest that the
economic argument underpinning the widespread use of TNF inhibitors in established RA is unsustainable. 相似文献
105.
Background
DNA Microarrays have become the standard method for large scale analyses of gene expression and epigenomics. The increasing complexity and inherent noisiness of the generated data makes visual data exploration ever more important. Fast deployment of new methods as well as a combination of predefined, easy to apply methods with programmer's access to the data are important requirements for any analysis framework. Mayday is an open source platform with emphasis on visual data exploration and analysis. Many built-in methods for clustering, machine learning and classification are provided for dissecting complex datasets. Plugins can easily be written to extend Mayday's functionality in a large number of ways. As Java program, Mayday is platform-independent and can be used as Java WebStart application without any installation. Mayday can import data from several file formats, database connectivity is included for efficient data organization. Numerous interactive visualization tools, including box plots, profile plots, principal component plots and a heatmap are available, can be enhanced with metadata and exported as publication quality vector files. 相似文献106.
107.
108.
Céline Fouquet Bénédicte M. Babayan Aurélie Watilliaux Bruno Bontempi Christine Tobin Laure Rondi-Reig 《PloS one》2013,8(6)
We investigated the neural bases of navigation based on spatial or sequential egocentric representation during the completion of the starmaze, a complex goal-directed navigation task. In this maze, mice had to swim along a path composed of three choice points to find a hidden platform. As reported previously, this task can be solved by using two hippocampal-dependent strategies encoded in parallel i) the allocentric strategy requiring encoding of the contextual information, and ii) the sequential egocentric strategy requiring temporal encoding of a sequence of successive body movements associated to specific choice points. Mice were trained during one day and tested the following day in a single probe trial to reveal which of the two strategies was spontaneously preferred by each animal. Imaging of the activity-dependent gene c-fos revealed that both strategies are supported by an overlapping network involving the dorsal hippocampus, the dorsomedial striatum (DMS) and the medial prefrontal cortex. A significant higher activation of the ventral CA1 subregion was observed when mice used the sequential egocentric strategy. To investigate the potential different roles of the dorsal hippocampus and the DMS in both types of navigation, we performed region-specific excitotoxic lesions of each of these two structures. Dorsal hippocampus lesioned mice were unable to optimally learn the sequence but improved their performances by developing a serial strategy instead. DMS lesioned mice were severely impaired, failing to learn the task. Our data support the view that the hippocampus organizes information into a spatio-temporal representation, which can then be used by the DMS to perform goal-directed navigation. 相似文献
109.
Effect of pharmacological agents on the activity of the circular and longitudinal smooth muscle layers of human fallopian tube ampullar segments 总被引:1,自引:0,他引:1
The in vitro determination of the effects of some pharmacological agents on the outer diameter and axial tension of human Fallopian tube ampullar segments showed that some drugs may act on the circular and longitudinal smooth muscle layers relatively separately. PGF2 alpha elicited an excitatory response in both muscle layers while norepinephrine and isoproterenol decreased the activity. Oxytocin and indomethacin had relatively limited effects on the spontaneous motility of the ampullar segments. The calcium antagonist verapamil inhibited the spontaneous periodic activity. 相似文献
110.
Emin Oguzhan Oguz Hayati Yuksel Yasar Enli A. Cevik Tufan Gunfer Turgut 《Biological trace element research》2010,133(3):335-341
Copper is an essential trace element that is extremely toxic to organisms and organs at high doses. We have investigated the
histological and biochemical effects of a toxic dose of copper sulfate on the liver of term Ross broiler chicks. Fertilized
eggs were divided into three groups: experimental, injected with 50 mcg/0.1 ml copper sulfate in the air chambers on day 1;
sham, injected with 0.1 ml saline; and control, no injection. Term chicks were killed and their livers investigated histologically,
with hematoxylin–eosin-stained sections examined under light microscopy, and biochemically, for malondialdehyde and glutathione
levels. Histological examinations showed copper-treated samples with granular degeneration and necrosis of hepatocytes and
impairment to the cell lining of the remark cords. The samples had a congestive appearance, with blood in the vena centralis
and sinusoids, slight connective tissue increase, and lymphocyte infiltration. Control and sham group sections had normal
appearances. As oxidative damage parameters, in the copper-treated group, malondialdehyde levels were increased and glutathione
levels decreased. In the sham and control groups, there were no significant differences. At this toxic dose, copper sulfate
shows oxidative damage according to the histology of term chick liver that are confirmed biochemically by the changes in malondialdehyde
and glutathione levels. 相似文献