全文获取类型
收费全文 | 7866篇 |
免费 | 775篇 |
国内免费 | 4篇 |
出版年
2022年 | 51篇 |
2021年 | 122篇 |
2020年 | 74篇 |
2019年 | 87篇 |
2018年 | 122篇 |
2017年 | 116篇 |
2016年 | 191篇 |
2015年 | 306篇 |
2014年 | 334篇 |
2013年 | 452篇 |
2012年 | 516篇 |
2011年 | 495篇 |
2010年 | 320篇 |
2009年 | 331篇 |
2008年 | 485篇 |
2007年 | 414篇 |
2006年 | 359篇 |
2005年 | 417篇 |
2004年 | 387篇 |
2003年 | 407篇 |
2002年 | 347篇 |
2001年 | 133篇 |
2000年 | 111篇 |
1999年 | 124篇 |
1998年 | 120篇 |
1997年 | 107篇 |
1996年 | 85篇 |
1995年 | 77篇 |
1994年 | 89篇 |
1993年 | 84篇 |
1992年 | 74篇 |
1991年 | 74篇 |
1990年 | 63篇 |
1989年 | 65篇 |
1988年 | 80篇 |
1987年 | 86篇 |
1986年 | 65篇 |
1985年 | 80篇 |
1984年 | 48篇 |
1983年 | 54篇 |
1982年 | 60篇 |
1981年 | 63篇 |
1980年 | 50篇 |
1979年 | 42篇 |
1978年 | 39篇 |
1977年 | 36篇 |
1976年 | 33篇 |
1974年 | 29篇 |
1973年 | 31篇 |
1969年 | 33篇 |
排序方式: 共有8645条查询结果,搜索用时 31 毫秒
1.
2.
1. As trees age, they undergo significant physiological and morphological changes. Nevertheless, tree ontogeny and its impacts on herbivores are often overlooked as determinants of plant–herbivore population dynamics and the strength of plant–herbivore interactions. 2. Juniperus (Cupressaceae) is a dominant, long‐lived conifer that serves as the sole host to a specialised assemblage of caterpillars. Over the past 150 years, several juniper species in western North America have expanded their geographic occupancy at local and regional scales, which has resulted in an increase in the number of immature trees on the landscape. Using assays in the laboratory, the effects of tree ontogeny on caterpillar performance and oviposition preference for two juniper specialist caterpillars, Callophrys gryneus (Lycaenidae) and Glena quinquelinearia (Geometridae), were examined. The study considered whether responses to tree ontogeny were consistent across caterpillar species and juniper host species. 3. Tree age was found to be a reliable predictor of caterpillar performance, with caterpillars developing more quickly and growing larger when fed foliage from young trees. Differences in the phytochemical diversity between foliage from trees of different ages might help to explain observed differences in caterpillar performance. Interestingly, the specialist butterfly, C. gryneus, displayed an oviposition preference for foliage from old‐growth Juniperus osteosperma trees, despite the fact that larvae of this species performed poorly on older trees. 4. It is concluded that young juniper trees are an important resource for the specialised Lepidopteran community and that tree ontogeny is an important component of intraspecific variation, which contributes to the structure of plant–herbivore communities. 相似文献
3.
4.
N. L. Biddington P. A. Brocklehurst A. S. Dearman Jane Dearman 《Physiologia plantarum》1982,55(4):407-410
Celery seeds ( Apium graveolens L.) given a germination induction period (3 days imbibition at 17°C in the light) could be prevented from germinating by up to 14 days subsequent exposure to high temperature (32°C), polyethylene glycol (PEG), abscisic acid (ABA) or dark (22°C). When the seeds were returned to 17°C in the light, germination occurred and, except for the high temperature treatment, was more rapid compared to seeds given a germination induction period only.
Celery seeds incubated for 3 days at 17°C in the light and then air-dried at 20°C germinated slowly when re-sown at 17°C in the light, and achieved only 19% germination after 21 days. Exposing the seeds to high temperature, PEG, ABA or dark for up to 14 days before drying maintained seed viability and subsequent germination was faster. The longer treatment periods gave increased benefit, and PEG was the most effective treatment. It is suggested that the effectiveness of the treatments in inducing dehydration tolerance relates to their ability to inhibit germination possibly via their prevention of cell expansion. 相似文献
Celery seeds incubated for 3 days at 17°C in the light and then air-dried at 20°C germinated slowly when re-sown at 17°C in the light, and achieved only 19% germination after 21 days. Exposing the seeds to high temperature, PEG, ABA or dark for up to 14 days before drying maintained seed viability and subsequent germination was faster. The longer treatment periods gave increased benefit, and PEG was the most effective treatment. It is suggested that the effectiveness of the treatments in inducing dehydration tolerance relates to their ability to inhibit germination possibly via their prevention of cell expansion. 相似文献
5.
6.
Oligomycin sensitivity conferral protein (OSCP), factor 6 (F6), and ATPase inhibitor protein are all components of the ATP synthase complex of bovine mitochondria. They are encoded in nuclear DNA. Complementary DNA clones encoding the precursors of these proteins have been isolated from a bovine library by using mixtures of synthetic oligonucleotides as hybridization probes, and their DNA sequences have been determined. The deduced protein sequences show that the OSCP, F6, and inhibitor proteins have N-terminal presequences of 23, 32, and 25 amino acids, respectively. These presequences are not present in the mature proteins. It is assumed that they serve to direct the proteins into the mitochondrial matrix. The cDNA clones have also been employed as hybridization probes to investigate the genetic complexity of the three proteins in cows and humans. These experiments indicate that the bovine and human inhibitor and bovine F6 proteins are encoded by single genes but suggest the possibility of the presence in both species of more than one gene (or pseudogenes) for the OSCP. 相似文献
8.
9.
10.
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