全文获取类型
收费全文 | 210907篇 |
免费 | 8846篇 |
国内免费 | 826篇 |
出版年
2023年 | 669篇 |
2022年 | 541篇 |
2021年 | 1283篇 |
2020年 | 1178篇 |
2019年 | 1213篇 |
2018年 | 13907篇 |
2017年 | 12521篇 |
2016年 | 10845篇 |
2015年 | 6433篇 |
2014年 | 6224篇 |
2013年 | 8281篇 |
2012年 | 13545篇 |
2011年 | 20784篇 |
2010年 | 16826篇 |
2009年 | 11979篇 |
2008年 | 16304篇 |
2007年 | 17613篇 |
2006年 | 6784篇 |
2005年 | 6577篇 |
2004年 | 6646篇 |
2003年 | 6231篇 |
2002年 | 5621篇 |
2001年 | 2542篇 |
2000年 | 2396篇 |
1999年 | 2012篇 |
1998年 | 937篇 |
1997年 | 732篇 |
1996年 | 659篇 |
1995年 | 653篇 |
1994年 | 678篇 |
1993年 | 552篇 |
1992年 | 1343篇 |
1991年 | 1257篇 |
1990年 | 1085篇 |
1989年 | 1012篇 |
1988年 | 956篇 |
1987年 | 807篇 |
1986年 | 713篇 |
1985年 | 807篇 |
1984年 | 716篇 |
1983年 | 595篇 |
1982年 | 472篇 |
1981年 | 443篇 |
1979年 | 589篇 |
1978年 | 466篇 |
1975年 | 458篇 |
1974年 | 456篇 |
1973年 | 464篇 |
1972年 | 586篇 |
1971年 | 624篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
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103.
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104.
Liver microsomal concentration of cytochrome P.450 is increased in animals which are fed diets rich in polyunsaturated fatty acids. On the other hand, the effects of phenobarbital are more important when the dietary fat is more unsaturated. The unsaturation index in liver microsomal phosphatidylcholines depends on the unsaturation of the dietary fats. The treatment with phenobarbital constantly results in a decrease of the unsaturation index of fatty acids both in lecithins and cephalins. The importance of the liver microsomal cytochrome P.450 increase and the importance of the unsaturation index decrease in liver microsomal lecithins, both promoted by phenobarbital, are in good agreement. 相似文献
105.
Georges Lantéri-Laura 《PSN》2003,1(3):39-47
The author describes the history of the concept of depression in modern psychiatry from the end of the Age of Enlightenment until today in three parts. In the first period (1793–1854), the opposition of general delusion (mania) and partial delusion (melancholia) prevails, without the problem of changes of the affective state being an issue. Only with the work of J. Guislain, and later of W. Griesinger, does the concept of mood disorders become a categorical form in mental pathology with the idea of psychological pain. The second period (1854–1926) is distinguished firstly by the works of J.P. Falret on circular insanity, and then those of V. Magnan, J. Ségnan, J. Séglas et Ph. Chaslin in France and E. Kraepelin in Germany. This period is characterized by the classical construction of periodic manicdepressive psychosis and takes into account the opposition of mania and melancholia. In the third period (1926–1977), the influences of phenomenology, psychoanalysis and structuralism predominate. Gradually melancholia loses its place at the core of this field, in favour of the concept of depression and this change now characterizes contemporary psychiatry. 相似文献
106.
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
107.
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108.
109.
110.
Roberto Chiussi 《Marine and Freshwater Behaviour and Physiology》2003,36(1):41-50
Behavioral responses of juveniles and adults of the mangrove crab Aratus pisonii (H. Milne Edwards, 1837) to black geometric shapes of equal surface area was measured. Crabs were tested either in presence or absence of chemicals generated from two common predator species, the portunid crab Callinectes ornatus Ordway, and the soapfish Haemulon aurolineatum Cuvier, 1830. The present study tested the hypothesis that A. pisonii (1) has the capacity to orient to visual cues; (2) it discriminates between different visual objects based on a combination of chemical and visual information and (3) this behavior changes with age. When presented with single black targets in background water, juveniles oriented toward all shapes. This behavioral response was interpreted as visual orientation toward potential shelter. Among shapes, juveniles showed preference for the vertical rectangle, probably due to the recognition of natural visual elements like mangrove roots. In predator conditioned water, juveniles exhibited a stronger response than in background water. Thus, juveniles were able to detect by odor the potential presence of predators. Change in responsiveness between adults and juveniles was also demonstrated. 相似文献