全文获取类型
收费全文 | 112805篇 |
免费 | 2213篇 |
国内免费 | 918篇 |
专业分类
115936篇 |
出版年
2023年 | 102篇 |
2022年 | 219篇 |
2021年 | 465篇 |
2020年 | 209篇 |
2019年 | 314篇 |
2018年 | 12124篇 |
2017年 | 10900篇 |
2016年 | 7958篇 |
2015年 | 1562篇 |
2014年 | 1349篇 |
2013年 | 1554篇 |
2012年 | 5882篇 |
2011年 | 14357篇 |
2010年 | 12996篇 |
2009年 | 9051篇 |
2008年 | 11056篇 |
2007年 | 12585篇 |
2006年 | 1462篇 |
2005年 | 1682篇 |
2004年 | 2103篇 |
2003年 | 2084篇 |
2002年 | 1787篇 |
2001年 | 422篇 |
2000年 | 254篇 |
1999年 | 225篇 |
1998年 | 262篇 |
1997年 | 177篇 |
1996年 | 145篇 |
1995年 | 123篇 |
1994年 | 120篇 |
1993年 | 141篇 |
1992年 | 112篇 |
1991年 | 129篇 |
1990年 | 87篇 |
1989年 | 72篇 |
1988年 | 70篇 |
1987年 | 72篇 |
1986年 | 47篇 |
1985年 | 65篇 |
1984年 | 72篇 |
1983年 | 86篇 |
1982年 | 79篇 |
1981年 | 74篇 |
1980年 | 75篇 |
1978年 | 65篇 |
1977年 | 43篇 |
1975年 | 42篇 |
1972年 | 258篇 |
1971年 | 280篇 |
1962年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Due to a long-term transgression since the Early Cambrian, an extensive shallow-water carbonate platform was developed in the entire Tarim Basin (NW China). During the deposition of the Yingshan Formation (Early-Middle Ordovician), a carbonate ramp system was formed in the intrashelf basin in the Bachu-Keping area of the western basin. Four well-exposed outcrop sections were selected to investigate their depositional facies, cycles, and sequences, as well as the depositional evolution. Detailed facies analyses permit the recognition of three depositional facies associations, including peritidal, semi-restricted subtidal, and open-marine subtidal facies, and eleven types of lithofacies. These are vertically arranged into meter-scale, shallowing-upward peritidal, semi-restricted subtidal, and open-marine subtidal cycles, in the span of Milankovitch frequency bands, suggesting a dominant control of Earth’s orbital forcing on the cyclic sedimentation on the platform. On the basis of vertical facies (or lithofacies) and cycle stacking patterns, as well as accommodation changes illustrated graphically by Fischer plots at all studied sections, six third-order depositional sequences are recognized and consist of lower transgressive and upper regressive parts. In shallow depositional settings, the transgressive packages are dominated by thicker-than-average, shallow subtidal cycles, whereas the regressive parts are mainly represented by thinner-than-average, relatively shallow subtidal to peritidal cycles. In relatively deep environments, however, the transgressive and regressive successions display the opposite trends of cycle stacking patterns, i.e., thinner-than-average subtidal cycles of transgressive packages. Sequence boundaries are mainly characterized by laterally traceable, transitional zones without apparent subaerial exposure features. Good correlation of the long-term changes in accommodation space inferred from vertical facies and cycle stacking patterns with sea-level fluctuations elsewhere around the world suggests an overriding eustatic control on cycle origination, platform building-up and evolution during the Early-Middle Ordovician, although with localized influences of syndepositional faulting and depositional settings. 相似文献
952.
The effect of algae on the production of musty-smelling compounds by actinomycetes was studied. Streptomyces spp., causing intensive musty odor, were isolated from hypertrophic Lake Kasumigaura and cultured in association with algae from the same lake. Isolate E and I effectively utilized the cyanobacteria, Microcystis aeruginosa and Anabaena spiroides, and the diatom, Synedra acus, as a carbon source and produced a musty-smelling 2-methylisoborneol in the shaken sediment cultures. High populations of algae and actinomycetes, and aerobic condition in the sediment seem responsible for the occurrence of musty odor in Lake Kasumigaura. 相似文献
953.
Tressia M. Dayton Karen A. Diefenbach Michelle L. Fuller Joshua Valtos Eric C. Niederhoffer 《Biometals》1996,9(2):131-137
Proteus mirabilis and Proteus vulgaris expressed a combination of superoxide dismutase (Sod) activities, which was assigned to FeSod1, FeSod2 and MnSod for P. mirabilis, and FeSod, MnSod and CuZnSod for P. vulgaris. Production of the Sod proteins was dependent on the availability of iron, whether cells were grown under anaerobiosis or aerobiosis and growth phase. Nalidixic acid and chloramphenicol inhibited cell growth and the iron- and dioxygen-dependent production of Sod. These results support the involvement of metal ions and redox status in the production of Proteus Sods. 相似文献
954.
Irwin J. Goldstein 《Journal of biosciences》1983,5(1):65-71
The physical-chemical and carbohydrate binding specificity ofGriffonia simplicifolia I (GS I) isolectins, one of the 4 lectins isolated fromGriffonia simplicifolia seeds, are described.Association constants for the binding of methyl α- and β-D-galactopyranoside and methyl 2-acetamido-2-deoxy-α-D-galactopyranoside to the A4, A2 B2 and B4 isolectins are reported.Precipitation reactions of theGriffonia simplicifolia isolectins with guaran and type B blood group substance are described.The hypothesis that subunit B is a precursor of subunit A, a process involving proteolytic cleavage of the B subunit, was tested by conducting structural studies on the 2 subunits. The results indicated that the A and B subunits are probably products of 2 separate but closely related, possibly contiguous genes. 相似文献
955.
Development and validation of a new dynamic computer‐controlled model of the human stomach and small intestine 下载免费PDF全文
956.
Alexander P. Drew Anthony N. Cutrupi Megan H. Brewer Garth A. Nicholson Marina L. Kennerson 《Human genetics》2016,135(11):1269-1278
Distal hereditary motor neuropathies predominantly affect the motor neurons of the peripheral nervous system leading to chronic disability. Using whole genome sequencing (WGS) we have identified a novel structural variation (SV) within the distal hereditary motor neuropathy locus on chromosome 7q34–q36.2 (DHMN1). The SV involves the insertion of a 1.35 Mb DNA fragment into the DHMN1 disease locus. The source of the inserted sequence is 2.3 Mb distal to the disease locus at chromosome 7q36.3. The insertion involves the duplication of five genes (LOC389602, RNF32, LMBR1, NOM1, MNX1) and partial duplication of UBE3C. The genomic structure of genes within the DHMN1 locus are not disrupted by the insertion and no disease causing point mutations within the locus were identified. This suggests the novel SV is the most likely DNA mutation disrupting the DHMN1 locus. Due to the size and position of the DNA insertion, the gene(s) directly affected by the genomic re-arrangement remains elusive. Our finding represents a new genetic cause for hereditary motor neuropathies and highlights the growing importance of interrogating the non-coding genome for SV mutations in families which have been excluded for genome wide coding mutations. 相似文献
957.
958.
959.
The hooded crow Corvus cornix is a west Palaearctic, solitary nesting, monogamous corvid. In the breeding season, populations are characterized by a social organization wherein breeding pairs are territorial and non-breeding individuals, called floaters, live in flocks. During a study of the breeding ecology of the hooded crow, conducted in a protected flooded area, we monitored nests with video cameras. We recorded two separate incidents when intruders attacked a female at the nest. We believe that she remained in the nest in order to prevent the strangers cannibalizing the nestlings by mantling over the brood. The spatio-temporal occurrence of these attacks suggests that the observed behaviour is intraspecific sexual aggression wherein non-breeding males mounted an immobilized female. 相似文献
960.
Jianzhong Xu Junlan Zhang Mei Han Weiguo Zhang 《Journal of industrial microbiology & biotechnology》2016,43(10):1417-1427
The gene integration method is an important tool to stably express desirable genes in bacteria. To avoid heavy workload and cost, we constructed a rapid and efficient method for genome modification. This method depended on a mobilizable plasmid, which contains a P tac promoter, an introduced multiple cloning site (iMCS), and rrnBT1T2 terminator. Briefly, the mobilizable plasmid pK18-MBPMT with the P tac-iMCS-rrnBT1T2 cartridge derived from pK18mobsacB was prepared to directly integrate hetero-/homologous DNA into the Corynebacterium glutamicum genome. Like our previous method, this method was based on insertional inactivation and double-crossover homologous recombination, which simultaneously achieved gene overexpression and inactivation in the genome without the use of genetic markers. Compared to the previous method, this protocol omitted the construction of a recombinant expression plasmid and clone of the target gene(s) cassette, which significantly decreased the workload, cost, and operational time. Using this method, the heterologous gene amy and the homologous gene lysC T311I were successfully integrated into the C. glutamicum genome at alaT and avtA loci, respectively. Moreover, the operation time of this method was shorter than that of the previous method, especially for repeated integration. This method, which is based on the mobilizable plasmid pK18-MBPMT, thus represents a potentially attractive protocol for the integration of genes in the course of genetic modification of C. glutamicum. 相似文献