全文获取类型
收费全文 | 8451篇 |
免费 | 783篇 |
国内免费 | 2篇 |
出版年
2023年 | 45篇 |
2022年 | 61篇 |
2021年 | 101篇 |
2020年 | 69篇 |
2019年 | 97篇 |
2018年 | 99篇 |
2017年 | 120篇 |
2016年 | 174篇 |
2015年 | 272篇 |
2014年 | 349篇 |
2013年 | 406篇 |
2012年 | 515篇 |
2011年 | 497篇 |
2010年 | 367篇 |
2009年 | 295篇 |
2008年 | 408篇 |
2007年 | 443篇 |
2006年 | 405篇 |
2005年 | 371篇 |
2004年 | 377篇 |
2003年 | 354篇 |
2002年 | 356篇 |
2001年 | 163篇 |
2000年 | 149篇 |
1999年 | 160篇 |
1998年 | 135篇 |
1997年 | 84篇 |
1996年 | 106篇 |
1995年 | 80篇 |
1994年 | 84篇 |
1993年 | 82篇 |
1992年 | 88篇 |
1991年 | 110篇 |
1990年 | 104篇 |
1989年 | 72篇 |
1988年 | 106篇 |
1987年 | 61篇 |
1986年 | 59篇 |
1985年 | 89篇 |
1984年 | 72篇 |
1983年 | 58篇 |
1982年 | 67篇 |
1981年 | 59篇 |
1980年 | 54篇 |
1979年 | 51篇 |
1977年 | 53篇 |
1976年 | 53篇 |
1975年 | 42篇 |
1974年 | 54篇 |
1972年 | 46篇 |
排序方式: 共有9236条查询结果,搜索用时 15 毫秒
281.
Pascal Bonnarme Serge Moukha Patrick Moreau Eric Record Laurence Lesage Claude Cassagne Marcel Asther 《FEMS microbiology letters》1994,120(1-2):155-161
Abstract Mycelia from the basidiomycete Phanerochaete chrysosporium , producing lignin and manganese peroxidases, were homogenized and fractionated on a sucrose gradient. The main subcellular fungal membrane fractions were successfully separated. Lipid composition analyses of the isolated membranes as well as associated marker enzymes distribution gave evidence to similarities with membranes originating from plants. Lignin and manganese peroxidases were investigated by immunodetection in subcellular fractions. Our results show that lignin and manganese peroxidases are mainly associated with Golgi apparatus vesicles and, to a lesser extent, with endoplasmic reticulum and light density vesicles, but not with plasma membranes. 相似文献
282.
283.
284.
285.
286.
Information structure facilitates communication between interlocutors by highlighting relevant information. It has previously been shown that information structure modulates the depth of semantic processing. Here we used event-related potentials to investigate whether information structure can modulate the depth of syntactic processing. In question-answer pairs, subtle (number agreement) or salient (phrase structure) syntactic violations were placed either in focus or out of focus through information structure marking. P600 effects to these violations reflect the depth of syntactic processing. For subtle violations, a P600 effect was observed in the focus condition, but not in the non-focus condition. For salient violations, comparable P600 effects were found in both conditions. These results indicate that information structure can modulate the depth of syntactic processing, but that this effect depends on the salience of the information. When subtle violations are not in focus, they are processed less elaborately. We label this phenomenon the Chomsky illusion. 相似文献
287.
Keith E. Arnold Steven N. Murray 《Journal of experimental marine biology and ecology》1980,43(2):183-192
Photosynthesis-irradiance relationships were determined in the field for five species of littoral and shallow sublittoral marine benthic green algae (Chlorophyta) of differing morphologies. Each species exhibited a linear increase in photosynthetic rate with increasing irradiance up to a maximum light-saturated value. Full sunlight (1405 to 1956 μE·m?2·s?1) inhibited photosynthesis of all species except the thick, optically dense, Codium fragile (Sur.) Har. Compensation irradiances ranged from 6.1 μE·m?2·s?1 for Enteromorpha intestinalis (L.) Link to 11.4 μE·m?2·s?1 for Ulva lobata (Kütz) S. & G. and did not reveal a consistent relationship to seaweed morphology. Saturation irradiances were determined statistically (Ik) and visually from graphical plots. with the latter technique resulting in values three to eight times higher and different comparative rankings of species than the former. Ik saturation irradiances were highest for Chaetomorpha linum (Müll.) Kütz. (81.9 μE·m?2·s?1) and lowest for Codium fragile (49.6 μE·m?2·s?1) and did not reveal a relationship with seaweed morphology. Regression equations describing light-limited photosynthetic rates and the relative magnitudes of the maximal net photosynthetic responses both strongly suggested a relationship with seaweed morphology. Highest net photosynthetic rates were obtained for the thin, sheet-like algae Ulva lobata (9.2 mg C·g dry wt?1·h?1), U. rigida C. Ag. (6.5 mg C·g dry wt?1·h?1) and the tubular form, Enteromorpha intestinalis (7.3 mg C·g dry wt?1·h?1), while lowest rates occurred for Codium fragile (0.9 mg C·g dry wt?1·h?1). Similarly, steepest light-limited slopes were found for the algae of simpler morphology, while the most gradual slope was determined for Codium fragile, the alga with greatest thallus complexity. 相似文献
288.
H. Ranneberg und C. G. Arnold 《Molecular & general genetics : MGG》1968,102(1):27-38
Summary In crosses of a p-aminobencoic acid requiring mutant of Chlamydomonas reinhard with the wildtype we observed besides the expected 4:4 segregation a surprisingly high frequency of aberrant segregation, all of which preferentially led to the wildtype. The only possible explanation of this finding is a non-reciprocal recombination, as mutations, trisomy and the loss of a tetrad cell with following additional division of a sister cell can be excluded. The molecular mechanism of non-reciprocal recombinations is still unknown. Nevertheless our findings are best understood, if we accept the hybrid-DNA model of Holliday, especially because this model is not only able to explain the 5:3 and 6:2 tetrads, but also the 7:1 and 8:0 segregations which occur at a much lower rate.The frequency of non-reciprocal recombinations could be reduced by irradiating zygotes at the very beginning of the germination period. If the X-rays were applicated 61/2 hours after induction of the germination, no clear aberrant segregation could be found.The reduction of the frequency of non-reciprocal recombinations by X-rays leads to the conclusion, that the mechanism of mutation and conversion are not identical. On the other hand we known many mutagenic substances which also cause non-reciprocal recombination. Thus it can be supposed that both the mechanisms have some steps in common. 相似文献
289.
290.
Geise Ribeiro Marcel Benadiba Denise de Oliveira Silva Alison Colquhoun 《Cell biochemistry and function》2010,28(1):15-23
The present study reports the synthesis of a novel compound with the formula [Ru2(aGLA)4Cl] according to elemental analyses data, referred to as Ru2GLA. The electronic spectra of Ru2GLA is typical of a mixed valent diruthenium(II,III) carboxylate. Ru2GLA was synthesized with the aim of combining and possibly improving the anti‐tumour properties of the two active components ruthenium and γ‐linolenic acid (GLA). The properties of Ru2GLA were tested in C6 rat glioma cells by analysing cell number, viability, lipid droplet formation, apoptosis, cell cycle distribution, mitochondrial membrane potential and reactive oxygen species. Ru2GLA inhibited cell proliferation in a time and concentration dependent manner. Nile Red staining suggested that Ru2GLA enters the cells and ICP‐AES elemental analysis found an increase in ruthenium from <0.02 to 425 mg/Kg in treated cells. The sub‐G1 apoptotic cell population was increased by Ru2GLA (22 ± 5.2%) when analysed by FACS and this was confirmed by Hoechst staining of nuclei. Mitochondrial membrane potential was decreased in the presence of Ru2GLA (44 ± 2.3%). In contrast, the cells which maintained a high mitochondrial membrane potential had an increase (18 ± 1.5%) in reactive oxygen species generation. Both decreased mitochondrial membrane potential and increased reactive oxygen species generation may be involved in triggering apoptosis in Ru2GLA exposed cells. The EC50 for Ru2GLA decreased with increasing time of exposure from 285 µM at 24 h, 211 µM at 48 h to 81 µM at 72 h. In conclusion, Ru2GLA is a novel drug with antiproliferative properties in C6 glioma cells and is a potential candidate for novel therapies in gliomas. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献