全文获取类型
收费全文 | 21074篇 |
免费 | 1061篇 |
国内免费 | 3067篇 |
出版年
2024年 | 39篇 |
2023年 | 254篇 |
2022年 | 376篇 |
2021年 | 494篇 |
2020年 | 483篇 |
2019年 | 654篇 |
2018年 | 524篇 |
2017年 | 556篇 |
2016年 | 610篇 |
2015年 | 750篇 |
2014年 | 980篇 |
2013年 | 1283篇 |
2012年 | 874篇 |
2011年 | 1015篇 |
2010年 | 857篇 |
2009年 | 1149篇 |
2008年 | 1258篇 |
2007年 | 1335篇 |
2006年 | 1235篇 |
2005年 | 1239篇 |
2004年 | 1102篇 |
2003年 | 1082篇 |
2002年 | 876篇 |
2001年 | 719篇 |
2000年 | 615篇 |
1999年 | 549篇 |
1998年 | 599篇 |
1997年 | 441篇 |
1996年 | 434篇 |
1995年 | 448篇 |
1994年 | 395篇 |
1993年 | 301篇 |
1992年 | 296篇 |
1991年 | 233篇 |
1990年 | 193篇 |
1989年 | 153篇 |
1988年 | 175篇 |
1987年 | 131篇 |
1986年 | 101篇 |
1985年 | 107篇 |
1984年 | 87篇 |
1983年 | 50篇 |
1982年 | 57篇 |
1981年 | 29篇 |
1980年 | 21篇 |
1979年 | 19篇 |
1978年 | 12篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1950年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Jürgen M. Schmitt Christine Michalowski Hans J. Bohnert 《Photosynthesis research》1988,17(1-2):159-171
Mesembryanthemum crystallinum responds to high salinity in the soil by shifting the mode of carbon assimilation from the C3 mode to Crassulacean acid metabolism (CAM). Several enzymes of carbon metabolism have increased apparent activities in the CAM mode, including phosphoenolpyruvate carboxylase (PEPcase) and pyruvate orthophosphate dikinase (PPDK). We have identified cDNA clones for PEPcase and PPDK by immunological screening of a cDNA library constructed in the protein expression vector lambda gt11. The clones were characterized by immunoblotting and RNA blotting techniques. RNA blotting showed that during CAM induction the steady-state level of mRNAs for both PEP case and PPDK increased.Abbreviations IPTG
isopropyl thiogalactoside
- PEP
phosphoenolpyruvate
- PEPcase
phosphoenolpyruvate carboxylase
- PPDK
pyruvate orthophosphate dikinase
- Xgal-5
bromo-4-chloro-3-indolyl-beta-D-galactopyranoside 相似文献
92.
93.
94.
95.
96.
97.
The ribulose-1,5-bisphosphate carboxylase (Rubisco) large- and small-subunit genes are encoded on the chloroplast genome of the eukaryotic chromophytic alga Olisthodiscus luteus. Northern blot experiments indicate that both genes are co-transcribed into a single (>6 kb) mRNA molecule. Clones from the O. luteus rbc gene region were constructed with deleted 5 non-coding regions and placed under control of the lac promoter, resulting in the expression of high levels of O. luteus Rubisco large and small subunits in Escherichia coli. Sucrose gradient centrifugation of soluble extracts fractionated a minute amount of carboxylase activity that cosedimented with native hexadecameric O. luteus Rubisco. Most of the large subunit synthesized in E. coli appeared insoluble or formed an aggregate with the small subunit possessing an altered charge: mass ratio compared to the native holoenzyme. The presence in O. luteus of a polypeptide that has an identical molecular mass and cross reacts with antiserum generated against pea large-subunit binding protein may indicate that a protein of similar function is required for Rubisco assembly in O. luteus. 相似文献
98.
99.
Patrick Dreyfus Dina Zevin-Sonkin Shlomo Seidman Catherine Prody Rivka Zisling Haim Zakut Hermona Soreq 《Journal of neurochemistry》1988,51(6):1858-1867
To study the polymorphism of human cholinesterases (ChEs) at the levels of primary sequence and three-dimensional structure, a fragment of human butyrylcholinesterase (BuChE) cDNA was subcloned into the pEX bacterial expression vector and its polypeptide product analyzed. Immunoblot analysis revealed that the clone-produced BuChE peptides interact specifically with antibodies against human and Torpedo acetylcholinesterase (AChE). Rabbit polyclonal antibodies prepared against the purified clone-produced BuChE polypeptides interacted in immunoblots with denatured serum BuChE as well as with purified and denatured erythrocyte AChE. In contrast, native BuChE tetramers from human serum, but not AChE dimers from erythrocytes, interacted with these antibodies in solution to produce antibody-enzyme complexes that could be precipitated by second antibodies and that sedimented faster than the native enzyme in sucrose gradient centrifugation. Furthermore, both AChE and BuChE dimers from muscle extracts, but not BuChE tetramers from muscle, interacted with these antibodies. To reveal further whether the anti-cloned BuChE antibodies would interact in situ with ChEs in the neuromuscular junction, bundles of muscle fibers were microscopically dissected from the region in fetal human diaphragm that is innervated by the phrenic nerve. Muscle fibers incubated with the antibodies and with 125I-Protein A were subjected to emulsion autoradiography, followed by cytochemical ChE staining. The anti-cloned BuChE antibodies, as well as anti-Torpedo AChE antibodies, created patches of silver grains in the muscle endplate region stained for ChE, under conditions where control sera did not. These findings demonstrate that the various forms of human AChE and BuChE in blood and in neuromuscular junctions share sequence homologies, but also display structural differences between distinct molecular forms within particular tissues, as well as between similarly sedimenting molecular forms from different tissues. 相似文献
100.
Alberto Abbruzzese 《Journal of neurochemistry》1988,50(3):695-699
Deoxyhypusine hydroxylase catalyzes the formation of hypusine from deoxyhypusine in a precursor form of eukaryotic initiation factor 4D (eIF-4D). The enzymatic activity was examined in mammalian brain homogenates and the results were consistent with the existence of deoxyhypusine hydroxylase levels comparable to those occurring in other mammalian tissues. Interspecies differences in the enzyme distribution were quite limited, with the highest specific activity values observed in cow brain (1.82 units/ mg of protein). In the rat the enzyme was found to be unevenly distributed among various brain regions. The parietal cortex contained the highest specific activity (2.1 units/mg of protein). Rat brain deoxyhypusine hydroxylase was mainly present in the postmicrosomal supernatant (81% of the total activity). The highest specific activity (3 units/mg of protein) was observed in the rat brain during the first few days of life. Thereafter the activity started to decline, and continued to do so for 15 days, remaining throughout the rest of life at levels of less than one-half that of newborn. 相似文献