全文获取类型
收费全文 | 24839篇 |
免费 | 1318篇 |
国内免费 | 28篇 |
出版年
2023年 | 184篇 |
2022年 | 257篇 |
2021年 | 747篇 |
2020年 | 487篇 |
2019年 | 522篇 |
2018年 | 768篇 |
2017年 | 701篇 |
2016年 | 950篇 |
2015年 | 1103篇 |
2014年 | 1399篇 |
2013年 | 1901篇 |
2012年 | 2035篇 |
2011年 | 1793篇 |
2010年 | 1083篇 |
2009年 | 937篇 |
2008年 | 1110篇 |
2007年 | 1082篇 |
2006年 | 890篇 |
2005年 | 886篇 |
2004年 | 700篇 |
2003年 | 646篇 |
2002年 | 577篇 |
2001年 | 479篇 |
2000年 | 429篇 |
1999年 | 390篇 |
1998年 | 168篇 |
1997年 | 127篇 |
1996年 | 121篇 |
1995年 | 126篇 |
1994年 | 108篇 |
1993年 | 97篇 |
1992年 | 268篇 |
1991年 | 229篇 |
1990年 | 236篇 |
1989年 | 183篇 |
1988年 | 225篇 |
1987年 | 188篇 |
1986年 | 155篇 |
1985年 | 168篇 |
1984年 | 165篇 |
1983年 | 111篇 |
1982年 | 106篇 |
1981年 | 135篇 |
1980年 | 110篇 |
1979年 | 151篇 |
1978年 | 97篇 |
1977年 | 107篇 |
1975年 | 92篇 |
1974年 | 86篇 |
1973年 | 76篇 |
排序方式: 共有10000条查询结果,搜索用时 22 毫秒
1.
2.
3.
4.
Abstract Competition experiments revealed that adenine and guanine were transported by a purine permease in both Candida glabrata 4 and a C. glabrata 4 cytosine permease negative mutant. The C. glabrata 4 cytosine permease negative mutant was isolated using 5-fluorocytosine selection. This mutant no longer transported cytosine, but transported adenine and guanine. A transport system for hypoxanthine was not detected. Hence, in addition to the cytosine permease, a purine permease exists in C. glabrata . This differs from the purine cytosine permeases in Saccharomyces cereuisiae and Candida albicans which transport adenine, cytosine, guanine and hypoxanthine. 相似文献
5.
6.
Pasupathi Sundaramoorthy Jae Jun Sim Yeong-Su Jang Siddhartha Kumar Mishra Keun-Yeong Jeong Poonam Mander Oh Byung Chul Won-Sik Shim Seung Hyun Oh Ky-Youb Nam Hwan Mook Kim 《PloS one》2015,10(1)
Cancer cell motility is a key phenomenon regulating invasion and metastasis. Focal adhesion kinase (FAK) plays a major role in cellular adhesion and metastasis of various cancers. The relationship between dietary supplementation of calcium and colon cancer has been extensively investigated. However, the effect of calcium (Ca2+) supplementation on calpain-FAK-motility is not clearly understood. We sought to identify the mechanism of FAK cleavage through Ca2+ bound lactate (CaLa), its downstream signaling and role in the motility of human colon cancer cells. We found that treating HCT116 and HT-29 cells with CaLa immediately increased the intracellular Ca2+ (iCa2+) levels for a prolonged period of time. Ca2+ influx induced cleavage of FAK into an N-terminal FAK (FERM domain) in a dose-dependent manner. Phosphorylated FAK (p-FAK) was also cleaved in to its p-N-terminal FAK. CaLa increased colon cancer cells motility. Calpeptin, a calpain inhibitor, reversed the effects of CaLa on FAK and pFAK cleavage in both cancer cell lines. The cleaved FAK translocates into the nucleus and modulates p53 stability through MDM2-associated ubiquitination. CaLa-induced Ca2+ influx increased the motility of colon cancer cells was mediated by calpain activity through FAK and pFAK protein destabilization. In conclusion, these results suggest that careful consideration may be given in deciding dietary Ca2+ supplementation to patient undergoing treatment for metastatic cancer. 相似文献
7.
This study was conducted to study the long-term impact of bioinoculants, Azotobacter chroococcum and arbuscular mycorrhizal fungi (AMF) on growth and biomass yield of Jatropha curcas grown in nursery and in field conditions. The experiment was set up in a randomized block design, and the following treatments was designed (T1 = control, T2 = Azotobacter, T3 = inoculation with AMF, and T4 = inoculation with Azotobacter + AMF). Data on various growth attributes (shoot height and shoot diameter) and biochemical parameters [leaf relative water content (LRWC), sugars, protein, and photosynthetic pigments] were recorded up to 6 months in the nursery and in the field (18 months). Results pertaining to morpho-physiological traits showed Azotobacter and AMF consortia increase shoot height, shoot diameter, LRWC, sugars, proteins, and photosynthetic pigments over control under nursery conditions. Besides enhancing the plant growth, these bioinoculants helped in better establishment of Jatropha plants under field conditions. A significant improvement in the shoot height, shoot diameter, fruit yield/plant, and seed yield (g)/plant was evident in 18-month-old Jatropha plants under field conditions when Azotobacter and AMF were co-inoculated. This work supports the application of bioinoculants for establishment of Jatropha curcas in semi-arid regions. 相似文献
8.
Marjan M. Tajrishi Jonghyun Shin Michal Hetman Ashok Kumar 《The Journal of biological chemistry》2014,289(29):19985-19999
9.
10.
Organelles such as endosomes and the Golgi apparatus play a critical role in regulating signal transmission to the nucleus. Recent experiments have shown that appropriate positioning of these organelles within the intracellular space is critical for effective signal regulation. To understand the mechanism behind this observation, we consider a reaction-diffusion model of an intracellular signaling cascade and investigate the effect on the signaling of intracellular regulation in the form of a small release of phosphorylated signaling protein, kinase, and/or phosphatase. Variational analysis is applied to characterize the most effective regions for the localization of this intracellular regulation. The results demonstrate that signals reaching the nucleus are most effectively regulated by localizing the release of phosphorylated substrate protein and kinase near the nucleus. Phosphatase release, on the other hand, is nearly equally effective throughout the intracellular space. The effectiveness of the intracellular regulation is affected strongly by the characteristics of signal propagation through the cascade. For signals that are amplified as they propagate through the cascade, reactions in the upstream levels of the cascade exhibit much larger sensitivities to regulation by release of phosphorylated substrate protein and kinase than downstream reactions. On the other hand, for signals that decay through the cascade, downstream reactions exhibit larger sensitivity than upstream reactions. For regulation by phosphatase release, all reactions within the cascade show large sensitivity for amplified signals but lose this sensitivity for decaying signals. We use the analysis to develop a simple model of endosome-mediated regulation of cell signaling. The results demonstrate that signal regulation by the modeled endosome is most effective when the endosome is positioned in the vicinity of the nucleus. The present findings may explain at least in part why endosomes in many cell types localize near the nucleus. 相似文献