全文获取类型
收费全文 | 6397篇 |
免费 | 516篇 |
国内免费 | 3篇 |
出版年
2022年 | 42篇 |
2021年 | 68篇 |
2020年 | 58篇 |
2019年 | 51篇 |
2018年 | 96篇 |
2017年 | 78篇 |
2016年 | 122篇 |
2015年 | 229篇 |
2014年 | 273篇 |
2013年 | 313篇 |
2012年 | 455篇 |
2011年 | 392篇 |
2010年 | 277篇 |
2009年 | 233篇 |
2008年 | 358篇 |
2007年 | 374篇 |
2006年 | 350篇 |
2005年 | 339篇 |
2004年 | 323篇 |
2003年 | 320篇 |
2002年 | 309篇 |
2001年 | 96篇 |
2000年 | 62篇 |
1999年 | 84篇 |
1998年 | 106篇 |
1997年 | 63篇 |
1996年 | 61篇 |
1995年 | 76篇 |
1994年 | 77篇 |
1993年 | 75篇 |
1992年 | 66篇 |
1991年 | 51篇 |
1990年 | 60篇 |
1989年 | 42篇 |
1988年 | 53篇 |
1987年 | 44篇 |
1986年 | 46篇 |
1985年 | 47篇 |
1984年 | 59篇 |
1983年 | 44篇 |
1982年 | 43篇 |
1981年 | 39篇 |
1980年 | 46篇 |
1979年 | 41篇 |
1978年 | 40篇 |
1977年 | 32篇 |
1974年 | 38篇 |
1972年 | 29篇 |
1970年 | 26篇 |
1969年 | 31篇 |
排序方式: 共有6916条查询结果,搜索用时 93 毫秒
141.
Four cases of Crouzon syndrome, one familial and three sporadic, were investigated for mutations in exon B of the fibroblast growth factor receptor 2 (FGFR2) gene. In the familial case, a mutation was found at codon 340 that exchanged tyrosine for histidine. Mutations at codon 342, detected in the three sporadic cases, replaced a cysteine by another amino acid. While three of the mutations have been described before, the fourth mutation, a CG transversion at codon 342 in one of the sporadic cases, has not been recognized previously. Compilation of all exon B mutations in Crouzon syndrome described to date revealed that 6 of the 8 sporadic and 2 of the 9 familial cases have mutations in codon 342. These mutations caused the substitution of cysteine for another amino acid. Given that a mutation in codon 342 was found in 8 out of 17 cases and that in 9 cases the mutation occurred at five additional positions, codon 342 of exon B of the FGFR2 gene may be predisposed to mutations in Crouzon syndrome. 相似文献
142.
Ulrich Flögel Thoralf Niendorf Nathalie Serkowa Annette Brand Joachim Henke Dieter Leibfritz 《Neurochemical research》1995,20(7):793-802
Diffusion-weighted in vivo1H-NMR spectroscopy of F98 glioma cells embedded in basement membrane gel threads showed that the initial cell swelling to about 180% of the original volume induced under hypotonic stress was followed by a regulatory volume decrease to nearly 100% of the control volume in Dulbecco's modified Eagle's medium (DMEM) but only to 130% in Krebs-Henseleit buffer (KHB, containing only glucose as a substrate) after 7 h. The initial cell shrinkage to approx. 70% induced by the hypertonic stress was compensated by a regulatory volume increase which after 7 h reached almost 100% of the control value in KHB and 75% in DMEM.1H-,13C-and31P-NMR spectroscopy of perchloric acid extracts showed that these volume regulatory processes were accompanied by pronounced changes in the content of organic osmolytes. Adaptation of intra- to extracellular osmolarity was preferentially mediated by a decrease in the cytosolic taurine level under hypotonic stress and by an intracellular accumulation of amino acids under hypertonic stress. If these solutes were not available in sufficient quantities (as in KHB), the osmolarity of the cytosol was increasingly modified by biosynthesis of products and intermediates of essential metabolic pathways, such as alanine, glutamate and glycerophosphocholine in addition to ethanolamine. The cellular nucleoside triphosphate level measured by in vivo31P-NMR spectroscopy indicated that the energy state of the cells was more easily sustained under hypotonic than hypertonic conditions.To whom to address reprint requests. 相似文献
143.
Summary New H2O-selective homonuclear and heteronuclear 2D NMR experiments have been designed for the observation of protein hydration (PHOGSY, Protein Hydration Observed by Gradient Spectroscop Y). These experiments utilize selective excitation of the H2O resonance and pulsed field gradients for coherence selection and efficient H2O suppression. The method allows for a rapid and sensitive detection of H2O molecules in labelled and unlabelled proteins. In addition it opens a way to measure the residence time of water bound to proteins. Its application to uniformly 15N-labelled FKBP-12 (FK-506 binding protein) is demonstrated. 相似文献
144.
Summary Deionized water as well as simulated and genuine fermentation media, which contained varying concentrations of benzaldehyde and 4-decanolide, were used to investigate the applicability of selected styrene-divinylbenzene resins for low pressure downflow adsorption of aroma compounds in a fixed bed. The effects of flow rate and matrix on the respective breakthrough curve slopes were examined using the LUB-and the MTZ-model. 相似文献
145.
One of three nuclear localization signals of maize Activator (Ac) transposase overlaps the DNA-binding domain 总被引:5,自引:0,他引:5
Ulrich Boehm Manfred Heinlein Ute Behrens Reinhard Kunze 《The Plant journal : for cell and molecular biology》1995,7(3):441-451
The nuclear localization sequences (NLSs) of the Ac transposase (TPase) protein have been characterized by indirect immunofluorescence detection of TPase deletion derivatives and TPase/β-glucuronidase (GUS) fusion proteins in transiently transfected Petunia cells. The TPase contains three NLSs near its amino-terminal end, NLS(44–62), NLS(159–178) and NLS(174–206), each of which is sufficient to redirect GUS to the nucleus. Deletion of the N-terminal 102 TPase residues including NLS(44–62) results in strongly reduced nuclear import of the truncated TPase. NLS(44–62) and NLS(159–178) are bipartite NLSs, whereas the structure of NLS(174–206) does not allow a classification into one of the three major NLS categories. NLS(174–206) overlaps with the basic DNA-binding domain of TPase. A substitution of two amino acids in this segment (HiS191→Arg and Arg193→His) results in a total loss of DNA-binding activity, but retains reduced NLS activity. Accordingly, the two functions can be separated. In addition, we show that a NLS-deficient 71 kDa TPase derivative is co-imported into the nucleus in the presence of wildtype TPase. 相似文献
146.
Zdena Ďuračková Klaus Felix L'ubica Feniková Iveta Kepštová Ján Labuda Ulrich Weser 《Biometals》1995,8(3):183-187
A pulse radiolytic study using the cyclic tetrameric Schiff base N-coordinated copper complex Cu(TAAB)2+ has been performed. The reaction of the Cu(TAAB)2+ complex with superoxide revealed pseudo first-order characteristics with the rate constant of k
2 = (2.9 ± 0.5) × 108 mol–1 s–1 dm3. The complex survive presence of competing serum albumin in physiological concentrations. The complex stability constant K = 1.15 × 1018 (log K = 18.06) is two orders of magnitude higher than that of Cu(II)-serum albumin (log K = 16.2). Transient changes of the stability during the oxidation/reduction process and in the presence of 600 /mol l–1 albumin did not affect significantly either the electronic absorption of the complex or its catalytic activity. 相似文献
147.
148.
Richard A. Siegel Eva-Marie Düker Eberhard Fuchs Ulrich Pahnke Wolfgang Wuttke 《Neurochemistry international》1984,6(6):783-789
The effects of acute and subchronic stress upon discrete cholecystokinin (CCK) and Substance P (SP) neuronal systems have been studied. Adult male rats were exposed to foot-shock stress for periods of 2, 4, 10, 30 or 60 min, immediately following which they were decapitated; brains were rapidly removed and frozen, and subsequently microdissected and extracted. CCK and SP were determined by RIA. In the olfactory tubercule, stress had no effect upon CCK content, but induced a rapid depletion of SP. In the prefrontal cortex, increased CCK concentrations were found following 30 min of stress exposure. In the medial septum, foot-shock led to a rapid increase in CCK content, and to a similar but delayed change in SP levels. A rapid rise in CCK concentrations was also seen in the lateral septum, but no stress effect whatsoever upon SP occurred in this structure. In the dentate gyrus, CCK exhibited a biphasic responsiveness to stress, while SP levels were increased only at the later time intervals. These data demonstrate that discrete CCK and SP neuronal systems are responsive to stress, and thereby support a functional role for these peptides in the processing of neural and hormonal signals by the CNS. 相似文献
149.
Sucrose transport has been investigated in vacuoles isolated from barley mesophyll protoplasts. Rates of sucrose transfer across the tonoplast were even higher in vitro than in vivo indicating that the sucrose transport system had not suffered damage during isolation of the vacuoles. Sucrose transport is carrier-mediated as shown by substrate saturation of transport and sensitivity to a metabolic inhibitor and to competitive substrates. A number of sugars, in particular maltose and raffinose, decreased uptake of sucrose. Sorbitol was slowly taken up but had no effect on sucrose transport. The SH-reagent p-chloromercuribenzene sulfonate inhibited sucrose uptake completely. The apparent Km of the carrier for sucrose uptake was 21 mM. Transport was neither influenced by ATP and pyrophosphate, with or without Mg2+ present, nor by protonophores and valinomycin (with K+ present). Apparently uptake was not energy dependent. Efflux experiments with preloaded vacuoles indicated that sucrose unloading from the isolated vavuoles is mediated by the same carrier which catalyses uptake. The vacuole of mesophyll cells appears to represent an intermediary storage compartment. Uptake of photosynthetic products into the vacuole during the light apparently minimizes osmotic swelling of the small cytosolic compartment of vacuolated leaf cells when photosynthetic productivity exceeds the capacity of the phloem for translocation of sugars.Abbreviations Hepes
4-(2-hydroxyethyl)-1-piperazincethane-sulfonic acid
- pCMBS
p-chloromercuribenzene sulfonate
Dedicated to Professor Dr. W. Simonis on the occasion of his 75th birthday 相似文献
150.
The usefulness of hybridization by protoplast fusion and mitotic segregation for the genetic analysis of the imperfect fodder yeastCandida maltosa was tested. Mitotically stable fusion hybrids were obtained with frequencies between 10–6 and 10–7. Complementation tests were performed by protoplast fusion. Substances that are known to induce frequent mitotic segregation in other yeast species such as benomyl, p-fluorophenylalanine, and acriflavine were ineffective inC. maltosa. UV irradiation induced mitotic segregation in up to 10%. This agent induced mainly mitotic crossing over inC. maltosa. Our data enabled the construction of the linkage group I with the sequenceCEN-ade-26-pro-1. 相似文献