全文获取类型
收费全文 | 3465篇 |
免费 | 327篇 |
专业分类
3792篇 |
出版年
2022年 | 31篇 |
2021年 | 61篇 |
2020年 | 28篇 |
2019年 | 42篇 |
2018年 | 72篇 |
2017年 | 61篇 |
2016年 | 98篇 |
2015年 | 132篇 |
2014年 | 170篇 |
2013年 | 195篇 |
2012年 | 291篇 |
2011年 | 267篇 |
2010年 | 161篇 |
2009年 | 155篇 |
2008年 | 211篇 |
2007年 | 191篇 |
2006年 | 196篇 |
2005年 | 188篇 |
2004年 | 166篇 |
2003年 | 172篇 |
2002年 | 137篇 |
2001年 | 53篇 |
2000年 | 44篇 |
1999年 | 47篇 |
1998年 | 29篇 |
1997年 | 29篇 |
1996年 | 19篇 |
1995年 | 12篇 |
1994年 | 15篇 |
1993年 | 21篇 |
1992年 | 19篇 |
1991年 | 21篇 |
1990年 | 22篇 |
1989年 | 18篇 |
1988年 | 18篇 |
1987年 | 31篇 |
1986年 | 16篇 |
1984年 | 16篇 |
1982年 | 14篇 |
1980年 | 15篇 |
1979年 | 21篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1974年 | 13篇 |
1973年 | 14篇 |
1972年 | 12篇 |
1971年 | 17篇 |
1970年 | 15篇 |
1969年 | 15篇 |
1967年 | 15篇 |
排序方式: 共有3792条查询结果,搜索用时 15 毫秒
991.
992.
Carsten Thye Hansen Christian Overgaard Nielsen Rune Dietz Martin Munk Hansen 《Polar Biology》1990,10(7):529-539
Summary Samples of muscle, liver and kidney from 24 minke whales (Balaenoptera acutorostrata), 43 belugas (Delphinapterus leucas), and 98 narwhals (Monodon monoceros) were analyzed for zinc, cadmium, mercury, and selenium. Highly significant age accumulation of mercury was found. A lower level of significance of age accumulation of cadmium in belugas and narwhals is probably due to the fact that some of the highest cadmium concentrations are in subadults and young adults. The maximum concentrations of cadmium and mercury are very high: 1.68, 73.7, and 125 g cadmium, and 9.88, 42.8, and 4.61 g mercury per g wet weight of narwhal muscle, liver and kidney, respectively. The cadmium concentrations are correlated in the three organs, as are mercury and to a lesser extent selenium concentrations. The concentrations of mercury and selenium in liver are highly correlated. 相似文献
993.
Federica Ferrigno Danila Branca Olaf Kinzel Samuele Lillini Laura Llauger Bufi Edith Monteagudo Ester Muraglia Michael Rowley Carsten Schultz-Fademrecht Carlo Toniatti Caterina Torrisi Philip Jones 《Bioorganic & medicinal chemistry letters》2010,20(3):1100-1105
We describe an extensive SAR study in the 6-[4-fluoro-3-(substituted)benzyl]-4,5-dimethylpyridazin-3(2H)-one series which led to the identification of potent PARP-1 inhibitors, capable of inhibiting the proliferation of BRCA-1 deficient cancer cells in the low nanomolar range, and displaying >100-fold selectivity over the BRCA wild type counterparts. The series of compounds was devoid of hERG channel activity, and CYP inhibition and induction liabilities. Several analogs were stable in rat and human liver microsomes and displayed moderate rat clearance, with urinary excretion of parent as the major route of elimination. 相似文献
994.
Insulin and progesterone activate a common synthetic ribosomal protein S6 peptide kinase in Xenopus oocytes 总被引:3,自引:0,他引:3
A synthetic peptide Arg-Arg-Leu-Ser-Ser-Leu-Arg-Ala, the structure of which is based on that of a phosphorylated sequence in ribosomal protein S6, was employed as a probe for stimulated kinase activity in Xenopus laevis oocytes induced to mature with insulin or progesterone. Insulin elicited an early (20-30 min) 3-fold stimulation of S6 peptide phosphorylating activity that was not evident with progesterone. However, both hormones produced a delayed 7-12-fold stimulation of S6 peptide phosphorylating activity at the time of germinal vesicle breakdown. The results of DEAE-Sephacel, Sephacryl S-200, TSK-400, and heparin-Sepharose chromatographic fractionation experiments imply that a common S6 peptide kinase is activated as a consequence of short and long term insulin exposure, as well as in long term progesterone treatment of oocytes. Omission of potassium from the oocyte culture medium greatly facilitated insulin-induced meiotic maturation. 相似文献
995.
996.
Müller WE Schlossmacher U Eckert C Krasko A Boreiko A Ushijima H Wolf SE Tremel W Müller IM Schröder HC 《European journal of cell biology》2007,86(8):473-487
The skeleton of the siliceous sponges (Porifera: Hexactinellida and Demospongiae) is supported by spicules composed of bio-silica. In the axial canals of megascleres, harboring the axial filaments, three isoforms of the enzyme silicatein (-alpha, -beta and -gamma) have been identified until now, using the demosponges Tethya aurantium and Suberites domuncula. Here we describe the composition of the proteinaceous components of the axial filament from small spicules, the microscleres, in the demosponge Geodia cydonium that possesses megascleres and microscleres. The morphology of the different spicule types is described. Also in G. cydonium the synthesis of the spicules starts intracellularly and they are subsequently extruded to the extracellular space. In contrast to the composition of the silicateins in the megascleres (isoforms: -alpha, -beta and -gamma), the axial filaments of the microscleres contain only one form of silicatein, termed silicatein-alpha/beta, with a size of 25kDa. Silicatein-alpha/beta undergoes three phosphorylation steps. The gene encoding silicatein-alpha/beta was identified and found to comprise the same characteristic sites, described previously for silicateins-alpha or -beta. It is hypothesized, that the different composition of the axial filaments, with respect to silicateins, contributes to the morphology of the different types of spicules. 相似文献
997.
Soil organic carbon stability in forests: Distinct effects of tree species identity and traits 总被引:2,自引:0,他引:2
998.
999.
Naur P Hansen CH Bak S Hansen BG Jensen NB Nielsen HL Halkier BA 《Archives of biochemistry and biophysics》2003,409(1):235-241
The cytochrome P450 CYP79B1 from Sinapis alba has been heterologously expressed in Escherichia coli and shown to catalyze the conversion of tryptophan to indole-3-acetaldoxime. Three expression constructs were made, one expressing the native protein and two expressing proteins with different N-terminal modifications. The native construct gave the highest yield as estimated by enzymatic activity per liter of culture. Spheroplasts of E. coli expressing CYP79B1 were reconstituted with the Arabidopsis thaliana NADPH:cytochrome P450 reductase ATR1 heterologously expressed in E. coli to obtain enzymatic activity. This indicates that the E. coli electron-donating system, flavodoxin/flavodoxin reductase, does not support CYP79B1 activity. Recombinant CYP79B1 has a K(m) for tryptophan of 29+/-2 microM and a V(max) of 36.5+/-0.7nmolh(-1)(mlculture)(-1). The identity at the amino acid level of CYP79B1 is, respectively, 93 and 84% to CYP79B2 and CYP79B3 from A. thaliana, and 96% to CYP79B5 (Accession No. AF453287) from Brassica napus. The CYP79B subfamily of cytochromes P450 is likely to constitute a group of orthologous genes in the biosynthesis of indole glucosinolates. 相似文献
1000.
Alexander Foertig Alexander Wagenpfahl Thiemo Gerbich David Cheyns Vladimir Dyakonov Carsten Deibel 《Liver Transplantation》2012,2(12):1483-1489
Nongeminate recombination in organic solar cells based on copper phthalocyanine (CuPc) and C60 is investigated. Two device architectures, the planar heterojunction (PHJ) and the bulk heterojunction (BHJ), are directly compared in view of differences in charge carrier decay dynamics. A combination of transient photovoltage (TPV) experiments, yielding the small perturbation charge carrier lifetime, and charge extraction measurements, providing the charge carrier density is applied. In organic solar cells, charge photogeneration and recombination primarily occur at the donor–acceptor heterointerface. Whereas the BHJ can often be approximated by an effective medium due to rather small scale phase separation, the PHJ has a well defined two‐dimensional heterointerface. In order to study nongeminate recombination dynamics in PHJ devices the charge accumulation at this interface is most relavent. As only the spatially averaged carrier concentration can be determined from extraction techniques, the charge carrier density at the interface nint is derived from the open circuit voltage. Comparing the experimental results with macroscopic device simulation, the differences of recombination and charge carrier densities in CuPc:C60 PHJ and BHJ devices are discussed with respect to the device performance. The open circuit voltage of BHJ is larger than for PHJ at low light intensities, but at 0.3 sun the situation is reversed: here, the PHJ can finally take advantage of its generally longer charge carrier lifetimes, as the active recombination region is smaller. 相似文献