全文获取类型
收费全文 | 12220篇 |
免费 | 289篇 |
国内免费 | 696篇 |
专业分类
13205篇 |
出版年
2024年 | 9篇 |
2023年 | 70篇 |
2022年 | 127篇 |
2021年 | 144篇 |
2020年 | 139篇 |
2019年 | 182篇 |
2018年 | 176篇 |
2017年 | 144篇 |
2016年 | 170篇 |
2015年 | 361篇 |
2014年 | 774篇 |
2013年 | 674篇 |
2012年 | 623篇 |
2011年 | 893篇 |
2010年 | 676篇 |
2009年 | 605篇 |
2008年 | 656篇 |
2007年 | 726篇 |
2006年 | 612篇 |
2005年 | 579篇 |
2004年 | 522篇 |
2003年 | 464篇 |
2002年 | 304篇 |
2001年 | 199篇 |
2000年 | 283篇 |
1999年 | 320篇 |
1998年 | 301篇 |
1997年 | 262篇 |
1996年 | 235篇 |
1995年 | 283篇 |
1994年 | 250篇 |
1993年 | 212篇 |
1992年 | 196篇 |
1991年 | 184篇 |
1990年 | 135篇 |
1989年 | 145篇 |
1988年 | 124篇 |
1987年 | 128篇 |
1986年 | 84篇 |
1985年 | 47篇 |
1984年 | 44篇 |
1983年 | 33篇 |
1982年 | 33篇 |
1981年 | 24篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1976年 | 5篇 |
1973年 | 5篇 |
1972年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
31.
32.
Two cDNA clones for the barley photosystem I polypeptide which migrates with an apparent molecular mass of 9.5 kDa on SDS-polyacrylamide gels have been isolated using antibodies and an oligonucleotide probe. The determined N-terminal amino acid sequence for the mature polypeptide confirms the identification of the clones. The 644 base-pair sequence of one of the clones contains one large open reading frame coding for a 14 882 Da precursor polypeptide. The molecular mass of the mature polypeptide is 10 193 Da. The hydropathy plot of the polypeptide shows one membrane-spanning region with a predicted -helix secondary structure. The gene for the 9.5 kDa polypeptide has been designated PsaH. 相似文献
33.
Masafumi Abe Naoya Nakamura Shirou Fukuhara Takamasa Hayashi Keiki Kawakami Kenkichi Kita Toshifumi Kinoshita Toyoro Ohsato Haruki Wakasa 《Virchows Archiv. B, Cell pathology including molecular pathology》1990,59(1):107-113
A new human acute lymphoblastic leukemia (ALL) cell line, designated HBL-3, was established from the bone marrow of a patient
with non-T-ALL. The HBL-3 cell line expressed B4 (CD 19), BA-1 (CD 24) and HLA-DR antigens, but not surface immunoglobulin
(SIg) or cytoplasmic immunoglobulin (CIg). The cell line lacked the common acute lymphoblastic leukemia antigen (CALLA) and
antigenic markers characteristic of T-cell and myeloid cell lineages. The HBL-3 cells had structural rearrangements of both
the homologous chromosome 9s, including a translocation with chromosome 1 which has been reported in a patient with common
ALL. The cell line had rearranged immunoglobulin heavy chain genes but retained germ-line κ light chain genes and germ-line
T-cell receptorβ- and γ-chain genes. The HBL-3 cell line was strongly positive for terminal deoxynucleotidyl transferase (TdT). These findings
indicate that the HBL-3 cell line is derived from the earliest B-cell committed to B-cell lineage. 相似文献
34.
The erythromycin resistance plasmid pSM752 carrying the cloned streptokinase gene, skc, was introduced by protoplast transformation into Streptococcus equisimilis H46A from which skc was originally cloned. Cells transiently supporting the replication of pSM752 gave rise to an erythromycin-resistant clone designated H46SM which was plasmid free and produced streptokinase at levels approximately twice as high as the wild type. Southern hybridization of total cell DNA with an skc-containing probe provided evidence for the duplication of the skc gene in the H46SM chromosome. The results, which have some bearing on industrial streptokinase production, can be best explained by a single cross-over event between the chromosome and the plasmid in the region of shared homology leading to the integration of pSM752 in a Campbell-like manner. 相似文献
35.
中国九个人群耵聍的遗传多态性 总被引:6,自引:2,他引:4
报道了九个人群的耵聍位点基因。计算表明中国各族人群在耵聍位点上的遗传分化程度非常大,固定指数F_(ST)=0.22。本文根据耵聍基因频率在我国和邻近地区的分布趋势,认为亚洲东北地区应是干型基因的起源地,目前世界上耵聍位点基因频率分布格局主要是基因扩散的结果,而非选择作用造成的。 相似文献
36.
Ichiro Yamato Hiro Nakamura Hiroshi Murakami Yasuhiro Anraku 《FEMS microbiology letters》1988,56(1):21-27
Abstract The cybB gene on a plasmid encoding cytochrome b 561 in Escherichia coli was disrupted by insertion of Kmrl determinant DNA. The cromosomal cybB gene was replaced by the inactivated cybB gene on the plasmid by homologous recombination using λ phage lysogenization and heat-induction. The replacement was confirmed by Southern and Western blotting analyses. Deficiency on the cybB gene product did not affect the growth properties of the cells, and the oxidase activities of the cells dependent on various substrates were similar to those of the parental strain. Cytochrome b 561 is concluded to be expressed in E. coli , but may not play a major role in cell growth. In the genetic map of E. coli , the cybB gene was determined by conjugational and transductional crosses to be at 31 min between trg and terC . 相似文献
37.
38.
Identification, cloning, nucleotide sequence and chromosomal map location of hns, the structural gene for Escherichia coli DNA-binding protein H-NS 总被引:10,自引:0,他引:10
Cynthia L. Pon Raffaele A. Calogero Claudio O. Gualerzi 《Molecular & general genetics : MGG》1988,212(2):199-202
Summary Beginning with a synthetic oligonucleotide probe derived from its amino acid sequence, we have identified, cloned and sequenced the hns gene encoding H-NS, an abundant Escherichia coli 15 kDa DNA-binding protein with a possible histone-like function. The amino acid sequence of the protein deduced from the nucleotide sequence is in full agreement with that determined for H-NS. By comparison of the restriction map of the cloned gene and of its neighboring regions with the physical map of E. coli K12 as well as by hybridization of the hns gene with restriction fragments derived from the total chromosome, we have located the hns gene oriented counterclockwise at 6.1 min on the E. coli chromosome, just before an IS30 insertion element. 相似文献
39.
Sacco C. de Vries Hilbert Booij Peter Meyerink Gert Huisman H. Dayton Wilde Terry L. Thomas Ab van Kammen 《Planta》1988,176(2):196-204
Embryogenic suspension cultures of domesticated carrot (Daucus carota L.) are characterized by the presence of proembryogenic masses (PEMs) from which somatic embryos develop under conditions of low cell density in the absence of phytohormones. A culture system, referred to as starting cultures, was developed that allowed analysis of the emergence of PEMs in newly initiated hypocotyl-derived suspension cultures. Embryogenic potential, reflected by the number of FEMs present, slowly increased in starting cultures over a period of six weeks. Addition of excreted, high-molecular-weight, heat-labile cell factors from an established embryogenic culture considerably accelerated the acquisition of embryogenic potential in starting cultures. Analysis of [35S]methionine-labeled proteins excreted into the medium revealed distinct changes concomitant with the acquisition of embryogenic potential in these cultures. Analysis of the pattern of gene expression by in-vitro translation of total cellular mRNA from starting cultures with different embryogenic potential and subsequent separation of the [35S]methionine-labeled products by two-dimensional polyacrylamide gel electrophoresis demonstrated a small number of abundant in-vitro-translation products to be present in somatic embryos and in embryogenic cells but absent in nonembryogenic cells. Several other in-vitro-translation products were present in explants, non-embryogenic and embryogenic cells but were absent in somatic embryos. Hybridization of an embryoregulated complementary-DNA sequence, Dc3, to RNA extracted from starting cultures showed that the corresponding gene is expressed in somatic embryos and PEMs but not in non-embryogenic cells.Abbreviations 2,4-D
2,4-dichlorophenoxyacetic acid
- cDNA
complementary DNA
- PAGE
polyacrylamide gel electrophoresis
- PEM
proembryogenic mass 相似文献
40.
Summary Transformation and regeneration procedures for obtaining transgenic Brassica rapa ssp. oleifera plants are described. Regeneration frequencies were increasedby using silver nitrate and by adjusting the duration of exposure to 2,4-D. For transformation, Agrobacterium tumefaciens strain EHA101 containing a binary plasmid with the neomycin phosphotransferase gene (NPT II) and the b-glucuronidase gene (GUS) was cocultivated with hypocotyl explants from the oilseed B. rapa cvs. Tobin and Emma. Transformed plants were obtained within three months of cocultivation. Transformation frequencies for the cultivars Tobin and Emma were 1–9%. Evidence for transformation was shown by NPT II dot blot assay, the GUS fluorometric assay, Southern analysis, and segregation of the kanamycin-resistance trait in the progeny. The transformation and regeneration procedure described here has been used routinely to transform two cultivars of B. rapa and 18 cultivars of B. napus. 相似文献