全文获取类型
收费全文 | 25533篇 |
免费 | 2119篇 |
国内免费 | 2078篇 |
出版年
2024年 | 66篇 |
2023年 | 351篇 |
2022年 | 803篇 |
2021年 | 1330篇 |
2020年 | 868篇 |
2019年 | 1056篇 |
2018年 | 1001篇 |
2017年 | 742篇 |
2016年 | 1054篇 |
2015年 | 1554篇 |
2014年 | 1831篇 |
2013年 | 1935篇 |
2012年 | 2368篇 |
2011年 | 2026篇 |
2010年 | 1284篇 |
2009年 | 1024篇 |
2008年 | 1393篇 |
2007年 | 1168篇 |
2006年 | 1056篇 |
2005年 | 898篇 |
2004年 | 745篇 |
2003年 | 636篇 |
2002年 | 581篇 |
2001年 | 490篇 |
2000年 | 378篇 |
1999年 | 431篇 |
1998年 | 256篇 |
1997年 | 218篇 |
1996年 | 255篇 |
1995年 | 205篇 |
1994年 | 253篇 |
1993年 | 152篇 |
1992年 | 220篇 |
1991年 | 184篇 |
1990年 | 175篇 |
1989年 | 114篇 |
1988年 | 83篇 |
1987年 | 75篇 |
1986年 | 49篇 |
1985年 | 63篇 |
1984年 | 48篇 |
1983年 | 39篇 |
1982年 | 37篇 |
1981年 | 24篇 |
1980年 | 16篇 |
1979年 | 25篇 |
1977年 | 15篇 |
1976年 | 16篇 |
1975年 | 15篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
121.
Y Lu B F O'Dowd H Orrego Y Israel 《Biochemical and biophysical research communications》1992,189(2):749-758
We have cloned and sequenced a full-length cDNA (1083 bp) encoding the human liver cystathionine-gamma-lyase enzyme (cystathionase). The human cystathionase sequence presented a substantial deletion of 132 bases (44 amino acids) compared to that reported for rat cystathionase, and of 135 bases (45 amino acids) compared to that reported for yeast cystathionase. After re-alignment for the missing nucleotides, the human cDNA sequence shows significant amino acid homology to that for the rat enzyme (85%) and the yeast enzyme (50%). A search for an undeleted cDNA, by the polymerase chain reaction, yielded a second clone which contained the missing 132 bases. Flanking nucleotides in the latter clone were identical to those in the cDNA clone containing the deletion. The two forms of human cystathionase deduced from the two cDNA clones may be derived from two different genes or may be splice variants. 相似文献
122.
Proliferating cell nuclear antigen (PCNA) and PCNA-dependent DNA polymerase delta were partially purified and characterized from rabbit bone marrow. Rabbit DNA polymerase delta sediments at 8.2 S upon glycerol density gradient centrifugation. Similar to calf thymus PCNA-dependent DNA polymerase delta, a 125-123-kDa doublet and 48-kDa polypeptides correlate with DNA polymerase activity. Western blotting of rabbit DNA polymerase delta with polyclonal antibody to calf thymus PCNA-dependent DNA polymerase delta gives the same results as calf thymus delta; the 125-123-kDa doublet is recognized. PCNA-dependent DNA polymerase delta is resistant to inhibition by dideoxynucleotides and is relatively insensitive to inhibition by N2-[p-(n-butyl)phenyl]dGTP. A 3'-->5' exonuclease copurifies with the DNA polymerase. The processivity of DNA polymerase delta alone is very low but greatly increases with the addition of PCNA from rabbit bone marrow or calf thymus. Comparative studies of the original DNA polymerase delta from rabbit bone marrow demonstrate a lack of recognition by antibodies to calf thymus delta and a high degree of processivity in the absence of PCNA. Additionally, the originally described DNA polymerase delta is a single polypeptide of 122 kDa. These features would recategorize the original delta to the epsilon category by recently proposed convention. PCNA-dependent DNA polymerase delta is a relatively minor component of rabbit bone marrow compared to DNA polymerase alpha and PCNA-independent DNA polymerase delta (epsilon), the relative proportions being alpha, 60%; delta, 7%; and epsilon, 30%. 相似文献
123.
The structure and complete nucleotide sequence of the avian lipoprotein lipase gene. 总被引:6,自引:0,他引:6
D A Cooper S C Lu R Viswanath R N Freiman A Bensadoun 《Biochimica et biophysica acta》1992,1129(2):166-171
124.
The effects of zinc and other divalent metals on the [125I]T3 binding to rat c-erbA alpha and beta recombinant proteins were assessed. The addition of ZnCl2 caused a reversible and dose-dependent inhibition of [125I]T3 binding to rc-erbA beta proteins with half maximum inhibition occurring at 50-100 microM, but no significant effect on [125I]T3 binding to rc-erbA alpha under the same assay conditions. Scatchard analysis revealed a decrease in [125I]T3 binding capacity to beta protein without marked change in Kd values in presence of zinc. Moreover, significant inhibitions of [125I]T3 binding to both alpha and beta proteins were observed in the presence of 100 microM of either MnCl2, CdCl2 or CuCl2, but not MgCl2. Thus, the selective effect of zinc compared to other divalent metals to inhibit T3 binding to rc-erbA beta, but not alpha, proteins was documented and suggest a possible regulatory role for zinc in modulating the intracellular action of thyroid hormone. 相似文献
125.
利用BA-Sepharose 4B亲和层析技术丛白百利烟草(Nicotiana tabacum Baibaili)愈伤组织细胞分离提纯了分子量为4400±100道尔顿的细胞分裂素结合蛋白(CB-蛋白)。在细胞表面、核糖体、线粒体、叶绿体和细胞核上以及在细胞液中都有CB-蛋白存在,而核糖体上的CB-蛋白含量量高。探讨了CB-蛋白的功能。 相似文献
126.
Provvidenti,R.(1980)和Green,S.K.(1985)先后用同一套鉴别寄主谱,研究了美国和我国台湾省的TuMV株系分化情况。本文用Green的方法,对由十省(市)7,982份病样中筛选出的19个TuMV主流分离物,在同一条件下进行了鉴定。结果表明,属于C_1株系的有黑_3分离物;属于C_4株系的有京_2、京_3、冀_2、宁_1(南京)、粤_1和川_1共6个分离物;属于C_5株系的有黑_1、辽_1、京_1、冀_1、沪_1、鲁_1、鲁_2共7个分离物。未检出C_2和C_3株系。黑_2、沪_2、宁_2和秦_1(陕西)共4个性状相近的分离物和冀_3分离物尚不能按Green的标准归类,暂分别定为C_(3-2)和C_6株系。此外,对Green氏方法应用于我国十字花科蔬菜TuMV株系分化研究中存在的问题作了讨论。 相似文献
127.
128.
K. S. Koch X. P. Lu D. A. Brenner G. H. Fey A. Martinez-Conde H. L. Leffert 《In vitro cellular & developmental biology. Plant》1990,26(12):1202-1202
The online version of the original article can be found at 相似文献
129.
An env gene derived from a primary human immunodeficiency virus type 1 isolate confers high in vivo replicative capacity to a chimeric simian/human immunodeficiency virus in rhesus monkeys. 总被引:7,自引:6,他引:1
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
K A Reimann J T Li G Voss C Lekutis K Tenner-Racz P Racz W Lin D C Montefiori D E Lee-Parritz Y Lu R G Collman J Sodroski N L Letvin 《Journal of virology》1996,70(5):3198-3206
To explore the roles played by specific human immunodeficiency virus type 1 (HIV-1) genes in determining the in vivo replicative capacity of AIDS viruses, we have examined the replication kinetics and virus-specific immune responses in rhesus monkeys following infection with two chimeric simian/human immunodeficiency viruses (SHIVs). These viruses were composed of simian immunodeficiency virus SIVmac239 expressing HIV-1 env and the associated auxiliary HIV-1 genes tat, vpu, and rep. Virus replication was assessed during primary infection of rhesus monkeys by measuring plasma SIVmac p27 levels and by quantifying virus replication in lymph nodes using in situ hybridization. SHIV-HXBc2, which expresses the HIV-1 env of a T-cell-tropic, laboratory-adapted strain of HIV-1 (HXBc2), replicated well in rhesus monkey peripheral blood leukocytes (PBL) in vitro but replicated only to low levels when inoculated in rhesus monkeys. In contrast, SHIV-89.6 was constructed with the HIV-1 env gene of a T-cell- and macrophage-tropic clone of a patient isolate of HIV-1 (89.6). This virus replicated to a lower level in monkey PBL in vitro but replicated to a higher degree in monkeys during primary infection. Moreover, monkeys infected with SHIV-89.6 developed an inversion in the PBL CD4/CD8 ratio coincident with the clearance of primary viremia. The differences in the in vivo consequences of infection by these two SHIVs could not be explained by differences in the immune responses elicited by these viruses, since infected animals had comparable type-specific neutralizing antibody titers, proliferative responses to recombinant HIV-1 gp120, and virus-specific cytolytic effector T-cell responses. With the demonstration that a chimeric SHIV can replicate to high levels during primary infection in rhesus monkeys, this model can now be used to define genetic determinants of HIV-1 pathogenicity. 相似文献
130.
Protease-induced infectivity of hepatitis B virus for a human hepatoblastoma cell line. 总被引:12,自引:4,他引:8
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The human hepatoblastoma cell line HepG2 produces and secretes hepatitis B virus (HBV) after transfection of cloned HBV DNA. Intact virions do not infect these cells, although they attach to the surface of the HepG2 cell through binding sites in the pre-S1 domain. Entry of enveloped virions into the cell often requires proteolytic cleavage of a viral surface protein that is involved in fusion between the cell membrane and the viral envelope. Recently, we observed pre-S-independent, nonspecific binding between hepatitis B surface (HBs) particles and HepG2 cells after treatment of HBs antigen particles with V8 protease, which cleaves next to a putative fusion sequence. Chymotrypsin removed this fusion sequence and did not induce binding. In this study, we postulate that lack of a suitable fusion-activating protease was the reason why the HepG2 cells were not susceptible to HBV. To test this hypothesis, virions were partially purified from the plasma of HBV carriers and treated with either staphylococcal V8 or porcine chymotrypsin protease. Protease-digested virus lost reactivity with pre-S2-specific antibody but remained morphologically intact as determined by electron microscopy. After separation from the proteases, virions were incubated with HepG2 cells at pH 5.5. Cultures inoculated with either intact or chymotrypsin-digested virus did not contain detectable levels of intracellular HBV DNA at any time following infection. However, in cultures inoculated with V8-digested virions, HBV-specific products, including covalently closed circular DNA, viral RNA, and viral pre-S2 antigen, could be detected in a time-dependent manner following infection. Immunofluorescence analysis revealed that 10 to 30% of the infected HepG2 cells produced HBV antigen. Persistent secretion of virus by the infected HepG2 cells lasted at least 14 days and was maintained during several reseeding steps. The results show that V8-digested HBV can productively infect tissue cultures of HepG2 cells. It is suggested that proteolysis-dependent exposure of a fusion domain within the envelope protein of HBV is necessary during natural infection. 相似文献