全文获取类型
收费全文 | 200942篇 |
免费 | 8149篇 |
国内免费 | 1469篇 |
专业分类
210560篇 |
出版年
2023年 | 689篇 |
2022年 | 677篇 |
2021年 | 1393篇 |
2020年 | 1203篇 |
2019年 | 1259篇 |
2018年 | 13803篇 |
2017年 | 12404篇 |
2016年 | 10551篇 |
2015年 | 5898篇 |
2014年 | 5784篇 |
2013年 | 7498篇 |
2012年 | 12697篇 |
2011年 | 20077篇 |
2010年 | 16402篇 |
2009年 | 11578篇 |
2008年 | 15634篇 |
2007年 | 17007篇 |
2006年 | 6071篇 |
2005年 | 5922篇 |
2004年 | 5970篇 |
2003年 | 5642篇 |
2002年 | 5013篇 |
2001年 | 2511篇 |
2000年 | 2390篇 |
1999年 | 1952篇 |
1998年 | 831篇 |
1997年 | 676篇 |
1996年 | 580篇 |
1995年 | 581篇 |
1994年 | 596篇 |
1993年 | 479篇 |
1992年 | 1297篇 |
1991年 | 1229篇 |
1990年 | 1063篇 |
1989年 | 979篇 |
1988年 | 924篇 |
1987年 | 782篇 |
1986年 | 710篇 |
1985年 | 780篇 |
1984年 | 689篇 |
1983年 | 574篇 |
1982年 | 434篇 |
1981年 | 422篇 |
1979年 | 573篇 |
1978年 | 440篇 |
1975年 | 438篇 |
1974年 | 447篇 |
1973年 | 456篇 |
1972年 | 579篇 |
1971年 | 618篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
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
43.
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
44.
45.
46.
47.
The purpose of this review is to provide a global perspective on Oncorhynchus salmonine introductions and put-and-take fisheries based on modern stocking programs, with special emphasis on freshwater
ecosystems. We survey the global introductions of nine selected salmonines of the genus Oncorhynchus: golden trout, cutthroat trout, pink salmon, chum salmon, coho salmon, masu/cherry salmon, rainbow trout/steelhead, sockeye
salmon/kokanee, and chinook salmon. The information is organized on a geographical basis by continent, and then by species
and chronology. Two different objectives and associated definitions of ‘success’ for introductions are distinguished: (a)
seed introduction: release of individuals with the purpose of creating a wild-reproducing, self-sustaining population; and
(b) put-and-take introduction: release of individuals with the purpose of maintaining some level of wild population abundance,
regardless of wild reproduction. We identify four major phenomena regarding global salmonine introductions: (1) general inadequacy
of documentation regarding introductions; (2) a fundamental disconnect between management actions and ecological consequences
of introductions; (3) the importance of global climate change on success of previous and future introductions; and (4) the
significance of aquaculture as a key uncertainty in accidental introductions. We conclude this review with a recognition of
the need to terminate ongoing stocking programs for introduced salmonines worldwide. 相似文献
48.
Following arteriolar occlusion, tissue oxygen concentration decreases and anoxic tissue eventually develops. Although anoxia
first appears in the region most distal to the capillary at the venous end, it eventually spreads throughout the entire region
of supply. In this paper the changing oxygen concentration, from the time of occlusion until the tissue is entirely anoxic,
is examined mathematically. The equations governing oxygen transport to tissue are solved by iterating a nonlinear integral
equation. This solution is valid until anoxia first appears. After anoxia develops it is necessary to solve a moving boundary
problem. This is done using the method of matched asymptotic expansions, and accurate solutions are obtained for a wide range
of physiological conditions. 相似文献
49.
M. T. Vénec-Peyré 《Coral reefs (Online)》1987,5(4):205-212
The discovery of epipsammitic Foraminifera in sediments of Moorea and Scilly (French Polynesia) and the study of close relationships between embedded specimens and host-grains indicate that some species participate in the weakening and subsequent breakdown of skeletal grains and consequently contribute to the production of silt-sized particles. The study of 36 stations around the islands shows the factors that control the distribution and abundance of this incrusted microfauna. Specimens are more abundant on sand particles larger than 1,000 microns and in the high energy areas; this abundance decreases with depth. The physiological mechanism of penetrations is presumably chemical, but each species apparently has its own process: complete dissolution with removal of ions for the cytoplasm of calcareous species; partial dissolution with transport of silt-size aggregates on the test of agglutinated species. The purpose of such penetration may be to protect themselves against water turbulence and to provide material for test construction. 相似文献
50.