全文获取类型
收费全文 | 7835篇 |
免费 | 1119篇 |
国内免费 | 1268篇 |
专业分类
10222篇 |
出版年
2024年 | 50篇 |
2023年 | 237篇 |
2022年 | 225篇 |
2021年 | 284篇 |
2020年 | 353篇 |
2019年 | 390篇 |
2018年 | 348篇 |
2017年 | 389篇 |
2016年 | 372篇 |
2015年 | 329篇 |
2014年 | 427篇 |
2013年 | 556篇 |
2012年 | 287篇 |
2011年 | 356篇 |
2010年 | 338篇 |
2009年 | 441篇 |
2008年 | 433篇 |
2007年 | 483篇 |
2006年 | 404篇 |
2005年 | 393篇 |
2004年 | 305篇 |
2003年 | 263篇 |
2002年 | 254篇 |
2001年 | 185篇 |
2000年 | 164篇 |
1999年 | 141篇 |
1998年 | 146篇 |
1997年 | 119篇 |
1996年 | 121篇 |
1995年 | 117篇 |
1994年 | 105篇 |
1993年 | 118篇 |
1992年 | 103篇 |
1991年 | 78篇 |
1990年 | 67篇 |
1989年 | 78篇 |
1988年 | 53篇 |
1987年 | 49篇 |
1986年 | 61篇 |
1985年 | 84篇 |
1984年 | 81篇 |
1983年 | 64篇 |
1982年 | 88篇 |
1981年 | 73篇 |
1980年 | 55篇 |
1979年 | 54篇 |
1978年 | 21篇 |
1977年 | 16篇 |
1974年 | 12篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
The rate of Hg2+-assisted chloride release from several mer-[CrCl(diamine)(triamine)]2+ complexes has been measured as a function of pressure, Hg2+ concentration and temperature. The calculated activation volumes are independent of [Hg2+] and temperature and kinetic parametes 104 kHg (25 °c) (M−1 s−1), ΔH‡ (kJ mol−1), ΔS‡ (J K−1 mol−1), ΔV‡ (cc mol−1) are: (en)(dpt): 6.44. 75.5, −52, −5.0; (ibn)(dpt): 5.81, 89.5, −6, −0.03; (Me2tn)(dpt): 22.2, 84.9, −11, −0.5; (tn)(dpt): 29.1, 87, −1, +0.3; (en)(2,3-tri): 1.94, 87.0, −24, −5.7; (en)(Medpt): 0.417, 94.6, −11, −0.8; (tn)(Medpt): 9.14, 98.3, +26, +1.8. 相似文献
122.
Genomic constructs comprising the ovine -lactoglobulin gene are expressed in a position-independent manner in the mammary gland of transgenic mice. In some lines however, constitutive low-level transgene expression was detected in all other tissues. This ectopic expression presumably represents a position-dependent phenomenon since it was observed in only a proportion (40%) of the lines generated. Different lines of BLG transgenic mice displayed similar temporal patterns of ectopic expression. This pattern differed from that of BLG in the mammary gland. These data imply that the DNA elements that direct position-independent expression of -lactoglobulin transgenes in the mammary gland do not have the ability to insulate them from position effects in other tissues. Furthermore, the relatively high frequency and constitutive nature of ectopic expression suggests that transgene integration may not be totally random. 相似文献
123.
124.
Husain D.R. Goutx M. Acquaviva M. Gilewicz M. Bertrand J.-C. 《World journal of microbiology & biotechnology》1997,13(5):587-590
Three hydrocarbon uptake modes (adherence, emulsification and solubilization) were identified and quantified in cells and supernatants of a mesophilic marine bacterium Pseudomonas nautica strain 617 grown on eicosane. The adherence capacity was related to the enrichment of cells with wax esters and glycolipids. The emulsifying activity was related to the presence of extracellular biosurfactants composed of proteins, carbohydrates and lipids (35:63:2). The intensity of substrate uptake modes was sensitive to temperatures currently found in the original environment of P. nautica (16°C, 20°C and 32°C). When temperature decreased, a significant increase in adherence and emulsifying activity was observed in relation to biochemical changes, whereas solubilizing activity decreased. The marine bacterium was able to degrade 53–59% eicosane at the end of exponential growth after 13, 5 and 3 days incubation at 16°C, 20°C and 32°C respectively. 相似文献
125.
D. Casane S. Boissinot B.H.-J. Chang L.C. Shimmin W.-H. Li 《Journal of molecular evolution》1997,45(3):216-226
We sequenced three argininosuccinate-synthetase-processed pseudogenes (ΨAS-A1, ΨAS-A3, ΨAS-3) and their noncoding flanking
sequences in human, orangutan, baboon, and colobus. Our data showed that these pseudogenes were incorporated into the genome
of the Old World monkeys after the divergence of the Old World and New World monkey lineages. These pseudogene flanking regions
show variable mutation rates and patterns. The variation in the G/C to A/T mutation rate (u) can account for the unequal GC contents at equilibrium: 34.9, 36.9, and 41.7% in the pseudogene ΨAS-A1, ΨAS-A3, and ΨAS-3
flanking regions, respectively. The A/T to G/C mutation rate (v) seems stable and the u/v ratios equal 1.9, 1.7, and 1.4 in the flanking regions of ΨAS-A1, ΨAS-A3, and ΨAS-3, respectively. These ``regional' variations
of the mutation rate affect the evolution of the pseudogenes, too. The ratio u/v being greater than 1.0 in each case, the overall mutation rate in the GC-rich pseudogenes is, as expected, higher than in
their GC-poor flanking regions. Moreover, a ``sequence effect' has been found. In the three cases examined u and v are higher (at least 20%) in the pseudogene than in its flanking region—i.e., the pseudogene appears as mutation ``hot'
spots embedded in ``cold' regions. This observation could be partly linked to the fact that the pseudogene flanking regions
are long-standing unconstrained DNA sequences, whereas the pseudogenes were relieved of selection on their coding functions
only around 30–40 million years ago. We suspect that relatively more mutable sites maintained unchanged during the evolution
of the argininosuccinate gene are able to change in the pseudogenes, such sites being eliminated or rare in the flanking regions
which have been void of strong selective constraints over a much longer period. Our results shed light on (1) the multiplicity
of factors that tune the spontaneous mutation rate and (2) the impact of the genomic position of a sequence on its evolution.
Received: 10 February 1997 / Accepted: 21 April 1997 相似文献
126.
KOLOTKIN, RONETTE L, SUSAN HEAD, ALAN BROOKHART. Construct validity of the Impact of Weight on Quality of Life questionnaire. The Impact of Weight on Quality of Life questionnaire (IWQOL) is a 74-item self-report, condition-specific instrument that (1) assesses the effect of weight on quality of life in eight key areas, and (2) may be used as a treatment outcome measure and/or an evaluation tool for healthcare policy makers and third-party payers. This study explores IWQOL construct validity and provides new information on internal consistency, treatment effects, and differences between men and women. IWQOL total scores correlated highly with other measures of overall quality of life, and subscale scores correlated well with counterparts in the assessment battery. Internal consistency estimates for the IWQOL scales generally were high. For the women, 4-week participants, and the total sample, pretreatment-posttreatment differences were significant for all IWQOL scales and total score. For men, treatment differences were significant for the total score and all subscales except for Work and Mobility. Treatment differences for 2-week participants were significant for all scales except for Work. Consistent with previous IWQOL study results, the Comfort With Food scale scores reflected more discomfort at posttreatment as compared with pretreatment. The IWQOL, already translated into French and Italian, currently is demonstrating clinical and research utility as a quality-of-life outcome measure for clinical trials of antiobesity drugs and surgical treatments for patients with obesity. 相似文献
127.
Water molecules participate in proteinase-inhibitor interactions: crystal structures of Leu18, Ala18, and Gly18 variants of turkey ovomucoid inhibitor third domain complexed with Streptomyces griseus proteinase B. 总被引:3,自引:3,他引:0 下载免费PDF全文
K. Huang W. Lu S. Anderson M. Laskowski Jr M. N. James 《Protein science : a publication of the Protein Society》1995,4(10):1985-1997
Crystal structures of the complexes of Streptomyces griseus proteinase B (SGPB) with three P1 variants of turkey ovomucoid inhibitor third domain (OMTKY3), Leu18, Ala18, and Gly18, have been determined and refined to high resolution. Comparisons among these structures and of each with native, uncomplexed SGPB reveal that each complex features a unique solvent structure in the S1 binding pocket. The number and relative positions of water molecules bound in the S1 binding pocket vary according to the size of the side chain of the P1 residue. Water molecules in the S1 binding pocket of SGPB are redistributed in response to the complex formation, probably to optimize hydrogen bonds between the enzyme and the inhibitor. There are extensive water-mediated hydrogen bonds in the interfaces of the complexes. In all complexes, Asn 36 of OMTKY3 participates in forming hydrogen bonds, via water molecules, with residues lining the S1 binding pocket of SGPB. For a homologous series of aliphatic straight side chains, Gly18, Ala18, Abu18, Ape18, and Ahp18 variants, the binding free energy is a linear function of the hydrophobic surface area buried in the interface of the corresponding complexes. The resulting constant of proportionality is 34.1 cal mol-1 A-2. These structures confirm that the binding of OMTKY3 to the preformed S1 pocket in SGPB involves no substantial structural disturbances that commonly occur in the site-directed mutagenesis studies of interior residues in other proteins, thus providing one of the most reliable assessments of the contribution of the hydrophobic effect to protein-complex stability. 相似文献
128.
A 500-MHz 1H-NMR study on the single-stranded DNA undecamer (11-mer) 5d AAGTGTGATAT is presented. Using a combination of one-dimensional pre-steady-state nuclear Overhauser enhancement (NOE) measurements and two-dimensional homonuclear J-correlated spectroscopy, virtually complete resonance assignments are obtained. The relative magnitudes of the intra- and internucleotide NOEs indicate that the overall structure of the single-stranded 11-mer is a right-handed B-type helix with extensive base stacking. Within this overall structure there is quite a large degree of variability, as exemplified by variations in glycosidic bond and sugar pucker conformations, most likely determined by base sequence.Abbreviations NOE
nuclear Overhauser effect
- COSY
twodimensional homonuclear J-correlated spectroscopy
- 11-mer
undecamer
- EDTA
sodium ethylenediamine tetraacetate
- HPLC
nigh-pressure liquid chromatography
- DSS
4,4-dimethylsilapentane-1-sulfonate 相似文献
129.
The rate of electron transfer through Photosystem I (reduced 2,6-dichlorophenol indophenol (DCIPH2 → methylviologen) in a low-salt thylakoid suspension is inhibited by Mg2+ both under light-limited and the light-saturated conditions, the magnitude of inhibition being the same. The 2,6-dichlorophenol indophenol (DCIP) concentration dependence of the light-saturated rate in the presence and in the absence of Mg2+ shows that the overall rate constant of the photoreaction is not altered by Mg2+. With N,N,N′,N′-tetramethyl-p-phenylenediamine or 2,3,5,6-tetramethylphenylenediamine as electron donor only the light-limited rate, not the light-saturated rate, is inhibited by Mg2+ and the magnitude of inhibition is the same as with DCIP as donor. The results are interpreted in terms of heterogeneous Photosystem I, consisting of two types, PS I-A and PS I-B, where PS I-A is involved in cation-regulation of excitation energy distribution and becomes unavailable for DCIPH2 → methyl viologen photoelectron transfer in the presence of Mg2+. 相似文献
130.
The ability of salts to inhibit the O2-evolution activity of PS II preparations is shown to parallel closely the Hofmeister series, suggesting that inhibition is related to the solubility of the 16, 24 and 33 kDa proteins in these salt solutions. An examination of the effect of salt inactivation on the low temperature multiline EPR signal indicates that the release of either the 16 and 24 kDa proteins, or additionally the 33 kDa protein blocks or greatly reduces the efficiency of the advancement of the water-splitting complex to the S2-state; under some conditions, this inhibition is reversible. 相似文献