全文获取类型
收费全文 | 45639篇 |
免费 | 4319篇 |
国内免费 | 33篇 |
专业分类
49991篇 |
出版年
2022年 | 282篇 |
2021年 | 611篇 |
2020年 | 345篇 |
2019年 | 420篇 |
2018年 | 567篇 |
2017年 | 530篇 |
2016年 | 948篇 |
2015年 | 1631篇 |
2014年 | 1785篇 |
2013年 | 2265篇 |
2012年 | 2807篇 |
2011年 | 2887篇 |
2010年 | 1880篇 |
2009年 | 1816篇 |
2008年 | 2643篇 |
2007年 | 2657篇 |
2006年 | 2580篇 |
2005年 | 2562篇 |
2004年 | 2501篇 |
2003年 | 2465篇 |
2002年 | 2415篇 |
2001年 | 536篇 |
2000年 | 438篇 |
1999年 | 605篇 |
1998年 | 696篇 |
1997年 | 501篇 |
1996年 | 446篇 |
1995年 | 439篇 |
1994年 | 415篇 |
1993年 | 429篇 |
1992年 | 374篇 |
1991年 | 339篇 |
1990年 | 373篇 |
1989年 | 287篇 |
1988年 | 328篇 |
1987年 | 306篇 |
1986年 | 290篇 |
1985年 | 359篇 |
1984年 | 402篇 |
1983年 | 365篇 |
1982年 | 457篇 |
1981年 | 457篇 |
1980年 | 436篇 |
1979年 | 296篇 |
1978年 | 326篇 |
1977年 | 282篇 |
1976年 | 295篇 |
1975年 | 229篇 |
1974年 | 304篇 |
1973年 | 268篇 |
排序方式: 共有10000条查询结果,搜索用时 6 毫秒
41.
42.
Xinzhu Deng David Michaelson Jason Tchieu Jin Cheng Diana Rothenstein Regina Feldman Sang-gyu Lee John Fuller Adriana Haimovitz-Friedman Lorenz Studer Simon Powell Zvi Fuks E. Jane Albert Hubbard Richard Kolesnick 《PloS one》2015,10(6)
Mammalian NOTCH1-4 receptors are all associated with human malignancy, although exact roles remain enigmatic. Here we employ glp-1(ar202), a temperature-sensitive gain-of-function C. elegans NOTCH mutant, to delineate NOTCH-driven tumor responses to radiotherapy. At ≤20°C, glp-1(ar202) is wild-type, whereas at 25°C it forms a germline stem cell⁄progenitor cell tumor reminiscent of human cancer. We identify a NOTCH tumor phenotype in which all tumor cells traffic rapidly to G2⁄M post-irradiation, attempt to repair DNA strand breaks exclusively via homology-driven repair, and when this fails die by mitotic death. Homology-driven repair inactivation is dramatically radiosensitizing. We show that these concepts translate directly to human cancer models. 相似文献
43.
44.
45.
International Research Ethics 总被引:2,自引:0,他引:2
This article provides a critical overview of the most important issues pertaining to the ongoing debate on international research ethics. It critically describes three problems of continuing concern: 1) the question of whether the distinction between therapeutic and non-therapeutic research should be upheld; 2) the questions of whether the currently demanded best proven diagnostic and therapeutic method of treatment for all research subjects is feasible both in developed and in developing countries, and whether it should be upheld; 3) the questions of who owns international research ethics guidelines and regulatory frameworks and, how decisions about changes to such international guidelines can possibly be achieved, given that it seems to be the case that genuine disagreement about issues of content is possible and likely. 相似文献
46.
John Llewelyn Benjamin L. Phillips Ross A. Alford Lin Schwarzkopf Richard Shine 《Oecologia》2010,162(2):343-348
Cane toads (Bufo marinus) are now moving about 5 times faster through tropical Australia than they did a half-century ago, during the early phases of toad invasion. Radio-tracking has revealed higher daily rates of displacement by toads at the invasion front compared to those from long-colonised areas: toads from frontal populations follow straighter paths, move more often, and move further per displacement than do toads from older (long-established) populations. Are these higher movement rates of invasion-front toads associated with modified locomotor performance (e.g. speed, endurance)? In an outdoor raceway, toads collected from the invasion front had similar speeds, but threefold greater endurance, compared to conspecifics collected from a long-established population. Thus, increased daily displacement in invasion-front toads does not appear to be driven by changes in locomotor speed. Instead, increased dispersal is associated with higher endurance, suggesting that invasion-front toads tend to spend more time moving than do their less dispersive conspecifics. Whether this increased endurance is a cause or consequence of behavioural shifts associated with rapid dispersal is unclear. Nonetheless, shifts in endurance between frontal and core populations of this invasive species point to the complex panoply of traits affected by selection for increased dispersal ability on expanding population fronts. 相似文献
47.
48.
49.
Plasma choline concentrations were measured in humans, rats, and rabbits within the first few hours of life, before any food was ingested. Neonatal animals and humans had markedly elevated plasma choline levels compared to adult animals or humans. Possible mechanisms responsible for this elevation are discussed and possible consequences for brain function, lung function, and growth are presented. 相似文献
50.