全文获取类型
收费全文 | 15635篇 |
免费 | 932篇 |
国内免费 | 43篇 |
出版年
2024年 | 23篇 |
2023年 | 181篇 |
2022年 | 284篇 |
2021年 | 812篇 |
2020年 | 602篇 |
2019年 | 813篇 |
2018年 | 760篇 |
2017年 | 553篇 |
2016年 | 743篇 |
2015年 | 845篇 |
2014年 | 1025篇 |
2013年 | 1277篇 |
2012年 | 1294篇 |
2011年 | 1183篇 |
2010年 | 680篇 |
2009年 | 558篇 |
2008年 | 671篇 |
2007年 | 680篇 |
2006年 | 592篇 |
2005年 | 563篇 |
2004年 | 432篇 |
2003年 | 349篇 |
2002年 | 309篇 |
2001年 | 125篇 |
2000年 | 111篇 |
1999年 | 99篇 |
1998年 | 80篇 |
1997年 | 47篇 |
1996年 | 49篇 |
1995年 | 47篇 |
1994年 | 33篇 |
1993年 | 40篇 |
1992年 | 53篇 |
1991年 | 54篇 |
1990年 | 51篇 |
1989年 | 52篇 |
1988年 | 48篇 |
1987年 | 45篇 |
1986年 | 42篇 |
1985年 | 50篇 |
1984年 | 45篇 |
1983年 | 34篇 |
1982年 | 27篇 |
1981年 | 31篇 |
1980年 | 19篇 |
1979年 | 18篇 |
1978年 | 21篇 |
1976年 | 25篇 |
1975年 | 19篇 |
1974年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
91.
Mohammad B. Rashid Katsuhiko Shirahige Naotake Ogasawara Hiroshi Yoshikawa 《Gene》1994,150(2):213-220
We have analyzed the relationship between autonomously replicating sequence (ARS) structure and function for three ARS (ARS605, ARS607 and ARS609) from chromosome VI of Saccharomyces cerevisiae by systematic XhoI-linker mutation in the ARS consensus sequence (ACS) and flanking sequences. All mutations that encroached upon the ACS destroyed ARS activity. DNA sequences stimulative for ARS function were identified on either side of the ACS of ARS605 and only on the 3'-side of the ACS of ARS607. In ARS609, however, no such stimulative sequences were observed. Base substitutions complementary to the wild-type sequence of those stimulative regions, in ARS605 and ARS607, that did not change the AG of unwinding nor affected ARS activity suggests that these regions have, at least, a function as DNA-unwinding elements (DUE). ARS605, ARS607 and ARS609 DNA are of low AG value and showed hypersensitivity to single-strand-specific nuclease when inserted in negatively supercoiled plasmid. Linker mutations inhibitory for ARS activity (5L11 and 7L14) also caused significant changes in local nucleotide (nt) sensitivity within the ACS and its adjoining regions. Complementary base substitutions, however, did not affect these changes in local nt sensitivity. These results imply that the stimulative regions flanking the ACS are necessary to produce an optimum conformation around the ACS which may be important for full ARS activity. 相似文献
92.
DNA fragments of around 200 base pair (average size) have been covalently crosslinked with 8-methoxypsoralen under 365 nm UV light. The photoadduct, induced antibodies in rabbits with a titer of > 1:12,800 by direct bindng ELISA. Binding data showed that the induced antibodies are conformation-specific recognizing restricted conformational change at site of crosslinking. Human autoantibodies against DNA, bound not only to native DNA but to the photomodified DNA fragment as well. In addition, binding patterns of SLE sera obtained from different patients were remarkably similar, indicating the recognition of altered conformation of the modified polymer by naturally occurring SLE anti-DNA autoantibodies. 相似文献
93.
A. V. Gussev N. M. Ali K. N. Abdul-Ameer S. M. Amin K. Molnár 《Systematic parasitology》1993,25(3):229-237
Four new Dactylogyrus species are described and two redescribed from cyprinids of the River Tigris, Iraq. These are as follows: Dactylogyrus barbioides n. sp. from Barbus grypus; D. orbus n. sp. from Barbus lacerta; D. barbuli n. sp. from Barbus barbulus; D. macrostomi n. sp. from Cyprinion macrostomi; D. pavlovskyi Bychowsky, 1949 from Barbus grypus and Barbus sharpeyi; and D. inutilis Bychowsky, 1949 from Barbus xanthopterus. A phylogenetic and zoogeographical analysis is presented. 相似文献
94.
Dipanwita Bhattacharya T.K. Dhar K.A.I. Siddiqui E. Ali 《Journal of applied microbiology》1994,77(2):129-133
The production of phaseolinone, a phytotoxic metabolite of Macrophomina phaseolina in infected Phaseolus mungo seeds grown on soil, was estimated by enzyme-linked immunosorbent assay and HPLC. The degree of inhibition of seed germination correlated well with the amount of toxin produced; 50% inhibition was observed at a toxin level of 2.1 μg g-1 of wet tissue. A comparison of the toxin-producing ability of nine isolates of the fungus obtained from different hosts and localities showed that the strain MPK'83 produced a significantly larger amount of the toxin, both in liquid culture and in infected seeds. The virulence of the isolates was related to their ability to produce phaseolinone. 相似文献
95.
96.
Mohsen A. F. El-Hazmi Hassan M. Bahakim Arjumand S. Warsy Abdulkarim Al-Momen Abdullah Al-Wazzan Ibrahim Al-Fawwaz Sameer Huraib Mohammad Harakati 《Molecular and cellular biochemistry》1993,124(1):17-22
Sickle cell anaemia (SCA) exhibits significant variations in clinical presentation in different populations for which several genetic factors including SCA-associated -and -thalassaemias, G-6-PD deficiency and elevated Hb F level have been implicated as possible ameliorating factors. Saudi Arabia is unique in that mild and severe forms of the disease occur at a high frequency. We investigated the G/A ratio and Hb F level and correlated these values with the severity of SCA. The results showed that Hb F level varies significantly in both groups of patients with no evident correlation with the mild clinical manifestations. However, G/A ratio correlated significantly with the disease severity where a high ratio was observed in patients with the mild and a low ratio in patients with the severe disease. The results are evaluated and discussed in the light of correlation studies and regression analysis. 相似文献
97.
Recurrent neural networks with full symmetric connectivity have been extensively studied as associative memories and pattern recognition devices. However, there is considerable evidence that sparse, asymmetrically connected, mainly excitatory networks with broadly directed inhibition are more consistent with biological reality. In this paper, we use the technique of return maps to study the dynamics of random networks with sparse, asymmetric connectivity and nonspecific inhibition. These networks show three qualitatively different kinds of behavior: fixed points, cycles of low period, and extremely long cycles verging on aperiodicity. Using statistical arguments, we relate these behaviors to network parameters and present empirical evidence for the accuracy of this statistical model. The model, in turn, leads to methods for controlling the level of activity in networks. Studying random, untrained networks provides an understanding of the intrinsic dynamics of these systems. Such dynamics could provide a substrate for the much more complex behavior shown when synaptic modification is allowed. 相似文献
98.
99.
Tamara Schmey Corinn Small Severin Einspanier Lina Muñoz Hoyoz Tahir Ali Soledad Gamboa Betty Mamani German C. Sepulveda Marco Thines Remco Stam 《Environmental microbiology》2023,25(10):1830-1846
The wild relatives of modern tomato crops are native to South America. These plants occur in habitats as different as the Andes and the Atacama Desert and are, to some degree, all susceptible to fungal pathogens of the genus Alternaria. Alternaria is a large genus. On tomatoes, several species cause early blight, leaf spots and other diseases. We collected Alternaria-like infection lesions from the leaves of eight wild tomato species from Chile and Peru. Using molecular barcoding markers, we characterized the pathogens. The infection lesions were caused predominantly by small-spored species of Alternaria of the section Alternaria, like A. alternata, but also by Stemphylium spp., Alternaria spp. from the section Ulocladioides and other related species. Morphological observations and an infection assay confirmed this. Comparative genetic diversity analyses show a larger diversity in this wild system than in studies of cultivated Solanum species. As A. alternata has been reported to be an increasing problem in cultivated tomatoes, investigating the evolutionary potential of this pathogen is not only interesting to scientists studying wild plant pathosystems. It could also inform crop protection and breeding programs to be aware of potential epidemics caused by species still confined to South America. 相似文献
100.
Sally Badawi Feda E. Mohamed Divya Saro Varghese Bassam R. Ali 《Traffic (Copenhagen, Denmark)》2023,24(8):312-333
Endoplasmic reticulum-associated protein degradation (ERAD) is a stringent quality control mechanism through which misfolded, unassembled and some native proteins are targeted for degradation to maintain appropriate cellular and organelle homeostasis. Several in vitro and in vivo ERAD-related studies have provided mechanistic insights into ERAD pathway activation and its consequent events; however, a majority of these have investigated the effect of ERAD substrates and their consequent diseases affecting the degradation process. In this review, we present all reported human single-gene disorders caused by genetic variation in genes that encode ERAD components rather than their substrates. Additionally, after extensive literature survey, we present various genetically manipulated higher cellular and mammalian animal models that lack specific components involved in various stages of the ERAD pathway. 相似文献