全文获取类型
收费全文 | 113256篇 |
免费 | 8643篇 |
国内免费 | 7161篇 |
专业分类
129060篇 |
出版年
2024年 | 221篇 |
2023年 | 1481篇 |
2022年 | 3306篇 |
2021年 | 5591篇 |
2020年 | 3672篇 |
2019年 | 4478篇 |
2018年 | 4454篇 |
2017年 | 3323篇 |
2016年 | 4712篇 |
2015年 | 6837篇 |
2014年 | 8061篇 |
2013年 | 8522篇 |
2012年 | 10180篇 |
2011年 | 9085篇 |
2010年 | 5595篇 |
2009年 | 4889篇 |
2008年 | 5740篇 |
2007年 | 5048篇 |
2006年 | 4479篇 |
2005年 | 3445篇 |
2004年 | 3011篇 |
2003年 | 2595篇 |
2002年 | 2270篇 |
2001年 | 2048篇 |
2000年 | 1907篇 |
1999年 | 1892篇 |
1998年 | 1053篇 |
1997年 | 1158篇 |
1996年 | 1046篇 |
1995年 | 940篇 |
1994年 | 959篇 |
1993年 | 682篇 |
1992年 | 1009篇 |
1991年 | 848篇 |
1990年 | 626篇 |
1989年 | 570篇 |
1988年 | 493篇 |
1987年 | 421篇 |
1986年 | 397篇 |
1985年 | 398篇 |
1984年 | 212篇 |
1983年 | 197篇 |
1982年 | 137篇 |
1981年 | 116篇 |
1980年 | 107篇 |
1979年 | 119篇 |
1978年 | 78篇 |
1977年 | 60篇 |
1974年 | 74篇 |
1972年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
881.
Mengchao Yu Jie Lun Hongwei Zhang Lei Wang Gang Zhang Haisheng Zhang Jing Fang 《Acta biochimica et biophysica Sinica》2021,(11):1417-1427
Cancer cells are often exposed to cell intrinsic stresses and environmental perturbations that may lead to accumulation of unfolded and/or misfolded proteins in... 相似文献
882.
Fabrice Roegiers Joshua Kavaler Nicholas Tolwinski Yu-Ting Chou Hong Duan Fernando Bejarano Diana Zitserman Eric C. Lai 《Genetics》2009,182(1):407-410
Forty years ago, a high frequency of lethal giant larvae (lgl) alleles in wild populations of Drosophila melanogaster was reported. This locus has been intensively studied for its roles in epithelial polarity, asymmetric neural divisions, and restriction of tissue proliferation. Here, we identify a high frequency of lgl alleles in the Bloomington second chromosome deficiency kit and the University of California at Los Angeles Bruinfly FRT40A-lethal P collection. These unrecognized aberrations confound the use of these workhorse collections for phenotypic screening or genetic mapping. In addition, we determined that independent alleles of insensitive, reported to affect asymmetric cell divisions during sensory organ development, carry lgl deletions that are responsible for the observed phenotypes. Taken together, these results encourage the routine testing of second chromosome stocks for second-site alleles of lgl. 相似文献
883.
Thirty-seven wild plants as food for Asian elephants in the field in Simao, Yunnan province, China and five cultivated plants
as food for captive elephants in the Beijing Zoo were collected and analyzed for their main nutrient components. Protein,
fat, fiber, dry material, ash as well as major microelements: calcium, kalium, zincum, sodium in the food were analyzed by
standard methodology. No significant differences were found between the wild plants taken in the field and forage provided
in captivity. However, the calcium content in the forage is significantly less than the average of those in the wild plants.
It is suggested that the increase in calcium intake may contribute to the relief of low plasma calcium diseases of elephants
in captivity.
Translated from Journal of Beijing Normal University (Natural Science), 2006, 42(2): 184–188 [译自: 北京师范大学学报 (自然科学版)] 相似文献
884.
In this report, we used genistein that was extracted from a Chinese herbal medicine Huaijiao (Sophora japonica – Leguminosae) to evulate its pharmacological function on anti-osteoporosis. This genistein is purified in a large-scale production from Huaijiao by a state-of-art method as described by Tian et al. [2004. The preparation of genistein and LC-MS/MS on-line analysis. Drug Devel. Res. 61, 6–12]. Chemical structure of the isolated genistein was examined by using various techniques including nuclear magnetic resonant spectrum, infrared absorption spectrum, ultraviolet absorption spectrum and mass spectrum, and was proved to be identical to those purified from soybean in a small scale as previously reported. We randomly divided female SD rats into 6 groups, including control, ovariectomized model, Nilestriol-treated, and three level of dosages of genistein-treated. We evaluated the pharmacological effects of genistein against osteoporosis by measuring the bone density of femur and bone mineral group including calcium, phosphorous, and magnesium. The consequences of genistein treatment on bone histology and morphology were also determined by measuring the trabcular area, thickness and number. Our results indicated that treatment with a 4.5 or 9 mg/kg dosage of genistein could also prevent osteoporosis significantly at the 4th week after treatment. In comparison with the anti-osteoporosis effects of soybean genistein, the genistein extracted from Huaijiao has the same beneficial effect on anti-osteoporosis. 相似文献
885.
The chitosan with three-dimensional porous structure greatly increased the effective electrode surface for loading of platinum
nanoparticles and promoted efficient electron transfer. The resulting biosensor had a response time (within 5 s) and a linear
response from 6 μM to 4.2 mM glucose with a detection limit of 2 μM (S/N = 3). Moreover, the methodology can be applied for
the immobilization of other enzymes. 相似文献
886.
887.
volume 218, contents 相似文献
888.
Clonal descent and microevolution of Neisseria meningitidis during 30 years of epidemic spread 总被引:3,自引:0,他引:3
Giovanna Morelli Burkhard Malorny Kerstin Müller rea Seiler Jian-Fu Wang Jesus del Valle & Mark Achtman 《Molecular microbiology》1997,25(6):1047-1064
Serogroup A meningococci of subgroups III, IV-1 and IV-2 are probably descended from a common ancestor that existed in the nineteenth century. The 10.5 kb sequences spanning five distinct chromosomal loci, encoding cell-surface antigens, a secreted protease or housekeeping genes and intergenic regions, were almost identical in strains of those subgroups isolated in 1966, 1966 and 1917 respectively. During the subsequent two to three decades, all of these loci varied as a result of mutation, translocation or import of DNA from unrelated neisseriae. Thus, microevolution occurs frequently in naturally transformable bacteria. Many variants were isolated only once or within a single geographical location and disappeared thereafter. Other variants achieved genetic fixation within months or a few years. The speed with which sequence variation is either eliminated or fixed may reflect sequential bottlenecks associated with epidemic spread and contrasts with the results of phylogenetic analyses from bacteria that do not cause epidemics. 相似文献
889.
890.