全文获取类型
收费全文 | 18302篇 |
免费 | 1656篇 |
国内免费 | 846篇 |
专业分类
20804篇 |
出版年
2024年 | 33篇 |
2023年 | 206篇 |
2022年 | 379篇 |
2021年 | 641篇 |
2020年 | 440篇 |
2019年 | 560篇 |
2018年 | 581篇 |
2017年 | 565篇 |
2016年 | 746篇 |
2015年 | 1137篇 |
2014年 | 1230篇 |
2013年 | 1425篇 |
2012年 | 1711篇 |
2011年 | 1604篇 |
2010年 | 1007篇 |
2009年 | 947篇 |
2008年 | 1096篇 |
2007年 | 989篇 |
2006年 | 954篇 |
2005年 | 793篇 |
2004年 | 738篇 |
2003年 | 636篇 |
2002年 | 598篇 |
2001年 | 183篇 |
2000年 | 107篇 |
1999年 | 142篇 |
1998年 | 170篇 |
1997年 | 139篇 |
1996年 | 99篇 |
1995年 | 91篇 |
1994年 | 78篇 |
1993年 | 91篇 |
1992年 | 66篇 |
1991年 | 64篇 |
1990年 | 56篇 |
1989年 | 40篇 |
1988年 | 36篇 |
1987年 | 34篇 |
1986年 | 26篇 |
1985年 | 54篇 |
1984年 | 45篇 |
1983年 | 26篇 |
1982年 | 28篇 |
1981年 | 33篇 |
1980年 | 28篇 |
1979年 | 19篇 |
1978年 | 17篇 |
1977年 | 20篇 |
1976年 | 18篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
The operation of a wastewater treatment plant treating effluents from a dairy laboratory was monitored by an advanced system. This plant comprises a 12 m(3) anaerobic filter (AF) reactor and a 28 m(3) sequential batch reactor (SBR) coupled in series and is equipped with the following on-line measurement devices: biogas flow meter, feed and recycling flow meters, temperature sensor, dissolved oxygen analyzer, and redox meter. Other parameters such as chemical oxygen demand (COD), volatile fatty acids (VFA), etc. were determined off-line. The plant has been in operation for 634 days, the influent flow rate being 6-8 m(3)/d. COD concentration of the influent ranged between 8 and 12 kg COD/m(3), resulting in COD values in the effluent around 50-200 mg/L. The behavior of the system was studied using the set of measurements collected by the data acquisition program especially developed for this purpose. Monitoring of variables such as anaerobic reactor temperature permitted the detection and prevention of several failures such as temperature shocks in the AF reactor. Besides, off-line measurements such as the alkalinity or the VFA content, together with the on-line measurements, provided immediate information about the state of the plant and the detection of several anomalies, such as organic overloads in the SBR, allowing the implementation of several fast control actions. 相似文献
972.
How biologically relevant are interaction-based modules in protein networks? 总被引:1,自引:1,他引:0 下载免费PDF全文
By applying a graph-based algorithm to yeast protein-interaction networks we have extracted modular structures and show that they can be validated using information from the phylogenetic conservation of the network components. We show that the module cores, the parts with the highest intramodular connectivity, are biologically relevant components of the networks. These constituents correlate only weakly with other levels of organization. We also discuss how such structures could be used for finding targets for antimicrobial drugs. 相似文献
973.
Interactions of GGA3 with the ubiquitin sorting machinery 总被引:1,自引:0,他引:1
The Golgi-localized, gamma-ear-containing, Arf-binding (GGA) proteins constitute a family of clathrin adaptors that are mainly associated with the trans-Golgi network (TGN) and mediate the sorting of mannose 6-phosphate receptors. This sorting is dependent on the interaction of the VHS domain of the GGAs with acidic-cluster-dileucine signals in the cytosolic tails of the receptors. Here we demonstrate the existence of another population of GGAs that are associated with early endosomes. RNA interference (RNAi) of GGA3 expression results in accumulation of the cation-independent mannose 6-phosphate receptor and internalized epidermal growth factor (EGF) within enlarged early endosomes. This perturbation impairs the degradation of internalized EGF, a process that is normally dependent on the sorting of ubiquitinated EGF receptors (EGFRs) to late endosomes. Protein interaction analyses show that the GGAs bind ubiquitin. The VHS and GAT domains of GGA3 are responsible for this binding, as well as for interactions with TSG101, a component of the ubiquitin-dependent sorting machinery. Thus, GGAs may have additional roles in sorting of ubiquitinated cargo. 相似文献
974.
975.
DNA double-strand breaks, recombination and synapsis: the timing of meiosis differs in grasshoppers and flies 下载免费PDF全文
Viera A Santos JL Page J Parra MT Calvente A Cifuentes M Gómez R Lira R Suja JA Rufas JS 《EMBO reports》2004,5(4):385-391
The temporal and functional relationships between DNA events of meiotic recombination and synaptonemal complex formation are a matter of discussion within the meiotic field. To analyse this subject in grasshoppers, organisms that have been considered as models for meiotic studies for many years, we have studied the localization of phosphorylated histone H2AX (gamma-H2AX), which marks the sites of double-strand breaks (DSBs), in combination with localization of cohesin SMC3 and recombinase Rad51. We show that the loss of gamma-H2AX staining is spatially and temporally linked to synapsis, and that in grasshoppers the initiation of recombination, produced as a consequence of DSB formation, precedes synapsis. This result supports the idea that grasshoppers display a pairing pathway that is not present in other insects such as Drosophila melanogaster, but is similar to those reported in yeast, mouse and Arabidopsis. In addition, we have observed the presence of gamma-H2AX in the X chromosome from zygotene to late pachytene, indicating that the function of H2AX phosphorylation during grasshopper spermatogenesis is not restricted to the formation of gamma-H2AX foci at DNA DSBs. 相似文献
976.
Zhang W Singam R Hellermann G Kong X Juan HS Lockey RF Wu SJ Porter K Mohapatra SS 《Genetic vaccines and therapy》2004,2(1):8-10
BACKGROUND: The need for safe and effective treatment of dengue virus (DEN), a class A agent that causes dengue hemorrhagic fever/dengue shock syndrome, has been a critical global priority. An effective vaccine for DEN is not yet available. In this study the possibility of attenuating DEN infection using adeno-associated virus (AAV)-encoded short interfering RNAs (siRNA) was examined in Vero cells and human dendritic cells (DCs). METHODS: A cassette encoding siRNA targeted to a 3' untranslated sequence common to all DEN serotypes was designed and tested for its ability to attenuate DEN infection by use of AAV delivery. RESULTS: Vero cells or DCs infected with AAV-siRNA showed a significant, dose-dependent reduction in DEN infection. Treatment of DCs with AAV-siRNA also decreased the DEN-induced apoptosis of DCs and did not induce significant inflammation. CONCLUSION: These results demonstrate that AAV-mediated siRNA delivery is capable of reducing DEN infection in cells and may be useful in decreasing DEN replication in humans. 相似文献
977.
Giménez-Abián JF Sumara I Hirota T Hauf S Gerlich D de la Torre C Ellenberg J Peters JM 《Current biology : CB》2004,14(13):1187-1193
Sister chromatid separation in anaphase depends on the removal of cohesin complexes from chromosomes. In vertebrates, the bulk of cohesin is already removed from chromosome arms during prophase and prometaphase, whereas cohesin remains at centromeres until metaphase, when cohesin is cleaved by the protease separase. In unperturbed mitoses, arm cohesion nevertheless persists throughout metaphase and is principally sufficient to maintain sister chromatid cohesion. How arm cohesion is maintained until metaphase is unknown. Here we show that small amounts of cohesin can be detected in the interchromatid region of metaphase chromosome arms. If prometaphase is prolonged by treatment of cells with microtubule poisons, these cohesin complexes dissociate from chromosome arms, and arm cohesion is dissolved. If cohesin dissociation in prometaphase-arrested cells is prevented by depletion of Plk1 or inhibition of Aurora B, arm cohesion is maintained. These observations imply that, in unperturbed mitoses, small amounts of cohesin maintain arm cohesion until metaphase. When cells lacking Plk1 and Aurora B activity enter anaphase, chromatids lose cohesin. This loss is prevented by proteasome inhibitors, implying that it depends on separase activation. Separase may therefore be able to cleave cohesin at centromeres and on chromosome arms. 相似文献
978.
979.
Tapia RA Salas C Morello A Maya JD Toro-Labbé A 《Bioorganic & medicinal chemistry》2004,12(9):2451-2458
The synthesis of dihydronaphthofurandione and dihydrofuroquinolinedione derivatives 4-11 was performed through Diels-Alder reactions of dihydrobenzofurandione 1 with several carbodienes and acrolein N,N-dimethylhydrazone. Then, the use of 5-bromobenzofurandione 2 toward 1,3-pentadiene and the 1-azadiene afforded quinones 6 and 11 with a total regioselectivity. All the prepared quinones were tested for trypanocidal activity in vitro against Trypanosoma epimastigotes, Tulahuen strain. Among the tested compounds, the furoquinolinediones 10 and 11 have shown potent trypanocidal activities but, only the 1,5-regioisomer (11) was found active as a redox cycling agent. Calculation of their stereoelectronic properties by the density-functional theory method provided a new insight for the trypanocidal activity of these heterocyclic quinones. 相似文献
980.
The splicing of many alternative exons in the precursor messenger RNA (pre-mRNA) is regulated by extracellular factors but the underlying molecular bases remain unclear. Here we report the differential regulation of Bcl-x pre-mRNA splicing by extracellular factors and their distinct requirements for pre-mRNA elements. In K562 leukemia cells, treatment with interleukin-6 (IL-6) or granulocyte-macrophage colony stimulating factor (GM-CSF) reduced the proportion of the Bcl-xL variant mRNA while treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA) had no effect. In U251 glioma cells, however, TPA efficiently increased the Bcl-xL level. These regulations were also seen for a transfected splicing reporter mini-gene. Further analyses of deletion mutants indicate that nucleotides 1-176 of the downstream intron are required for the IL-6 effect, whereas additional nucleotides 177-284 are essential for the GM-CSF effect. As for the TPA effect, only nucleotides 1-76 are required in the downstream intron. Thus, IL-6, GM-CSF and TPA differentially regulate Bcl-x splicing and require specific intronic pre-mRNA sequences for their respective effects. 相似文献