全文获取类型
收费全文 | 44779篇 |
免费 | 16926篇 |
国内免费 | 2073篇 |
出版年
2024年 | 41篇 |
2023年 | 239篇 |
2022年 | 585篇 |
2021年 | 1350篇 |
2020年 | 2775篇 |
2019年 | 4407篇 |
2018年 | 4510篇 |
2017年 | 4654篇 |
2016年 | 4807篇 |
2015年 | 5091篇 |
2014年 | 4959篇 |
2013年 | 5560篇 |
2012年 | 3591篇 |
2011年 | 3098篇 |
2010年 | 4025篇 |
2009年 | 2654篇 |
2008年 | 1825篇 |
2007年 | 1305篇 |
2006年 | 1132篇 |
2005年 | 1086篇 |
2004年 | 968篇 |
2003年 | 940篇 |
2002年 | 905篇 |
2001年 | 703篇 |
2000年 | 534篇 |
1999年 | 451篇 |
1998年 | 216篇 |
1997年 | 192篇 |
1996年 | 175篇 |
1995年 | 134篇 |
1994年 | 154篇 |
1993年 | 99篇 |
1992年 | 90篇 |
1991年 | 107篇 |
1990年 | 86篇 |
1989年 | 66篇 |
1988年 | 48篇 |
1987年 | 32篇 |
1986年 | 43篇 |
1985年 | 27篇 |
1984年 | 26篇 |
1983年 | 25篇 |
1982年 | 18篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1975年 | 4篇 |
1971年 | 4篇 |
1968年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
Cibacron blue T_3GA与溴化氰活化的Sepharose 4B偶联后,产生一种能有效地分离有机磷水解酶的吸附剂。用0.15mol/L MgCl_2溶液从黄杆菌P3—2细胞抽提出的粗酶液通过柱层析分离,即可得到纯化8倍、酶活性回收率为269.4%的纯酶制品。该酶制品用凝胶电泳测是均一的。 相似文献
142.
143.
Variable expression of latent membrane protein in nasopharyngeal carcinoma can be related to methylation status of the Epstein-Barr virus BNLF-1 5''-flanking region. 总被引:7,自引:5,他引:2
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)
L F Hu J Minarovits S L Cao B Contreras-Salazar L Rymo K Falk G Klein I Ernberg 《Journal of virology》1991,65(3):1558-1567
Seven virus-coded proteins, the nuclear proteins EBNA-1 to EBNA-6 and the latent membrane protein (LMP), are regularly expressed in Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines. In nasopharyngeal carcinoma (NPC), only EBNA-1 is regularly expressed; LMP is detected in about 65% of the tumors. In Burkitt's lymphoma tumors only EBNA-1 is expressed. We have recently shown that the methylation patterns of the EBV genome varied between these cell types. In virally transformed lymphoblastoid cell lines of normal origin, the EBV DNA is completely unmethylated. In contrast, in the Burkitt's lymphoma-derived cell line Rael and in a nude mouse-passaged NPC tumor, C15, there was an extensive methylation of CpG pairs. The methylation extended into the coding regions of the two expressed genes, EBNA-1 (in both tumor types) and LMP (in C15). Two presumptive control regions were exempted from this overall methylation: the oriP that contains both an origin of DNA replication and an EBNA-1-dependent enhancer and the 5'-flanking region of the BNLF-1 open reading frame that codes for LMP. The latter was only exempted in the LMP expressing NPC. We have now investigated the relation between expression of LMP and methylation of DNA in the 5'-flanking 1 kb region of BNLF-1, coding for LMP. LMP was methylated in 3 of 12 NPC biopsies that did not express LMP but was partially or totally unmethylated in the remaining 9 that expressed the protein. The three BNLF-1 exons were highly methylated in all the tumors. The oriP region was unmethylated in all the tumors, as in the previously studied Rael cell line and nude mouse-passaged NPC. Also, the BamHI W enhancer region involved in the expression of EBNA nuclear proteins was methylated. None of the biopsies expressed EBNA-2. Our data show that the EBV genomes are highly methylated in NPC tumors. The strong reverse correlation between the methylation of the putative control region of the LMP gene and the expression of LMP suggests that methylation has a role in the regulation of this gene. 相似文献
144.
Temporal comparison of recombination and synaptonemal complex formation during meiosis in S. cerevisiae 总被引:53,自引:0,他引:53
In synchronous cultures of S. cerevisiae undergoing meiosis, an early event in the meiotic recombination pathway, site-specific double strand breaks (DSBs), occurs early in prophase, in some instances well before tripartite synaptonemal complex (SC) begins to form. This observation, together with previous results, supports the view that events involving DSBs are required for SC formation. We discuss the possibility that the mitotic pathway for recombinational repair of DSBs served as the primordial mechanism for connecting homologous chromosomes during the evolution of meiosis. DSBs disappear during the period when tripartite SC structure is forming and elongating (zygotene); presumably, they are converted to another type of recombination intermediate. Neither DSBs nor mature recombinant molecules are present when SCs are full length (pachytene). Mature reciprocally recombinant molecules arise at the end of or just after pachytene. We suggest that the SC might coordinate recombinant maturation with other events of meiosis. 相似文献
145.
Yan Ming Ling Yihling Huang Shansheng Gong Shuqing Xu Zhenxing 《Biological trace element research》1991,29(3):281-288
Contents of Cu and Zn of into-pulmonary blood (IPB), out-pulmonary blood (OPB), Lung tissue, and supernatant and macrophages of Lung Lavage were determined in superior mesenteric artery occlusion (SMAO) shock of rabbits. Zn of pulmonary tissue was 11.42 +/- 0.60 and 14.52 +/- 1.78 (micrograms/g wet wt) in SMAO shock and control groups, respectively. Content of Zn was found to be lower, Cu was not changed, and Cu/Zn ratio increased in lung tissue in SMAO shock. Contents of Cu and Zn in other samples were not changed. The results suggest that lower Zn in lung tissue related to acute lung injury. 相似文献
146.
M. Yang Fang Ming J. Hubble A. D. Lockett R. R. Rathbone J. A. Howell 《Biotechnology Techniques》1992,6(5):409-412
A simple thermal monitoring technique has been successfully applied to an adsorption system using a novel ion exchanger with
a large internal void volume (voidage) which can be operated at high superficial velocity (SV). Temperature changes resulting
from heats of adsorption could be followed effectively using semi-conductor thermistor devices inserted into the resin through
the column wall. Results show that, despite the high feed rates adopted, the thermal signals generated can be consistently
related to the position of the breakthrough front within the bed. 相似文献
147.
G. H. Canullo R. Rodríguez‐kábana J. W. Kloepper 《Biocontrol Science and Technology》1992,2(2):159-169
The efficacy of 2‐furfuraldehyde for control of Sclerotium rolfsii was studied in laboratory and greenhouse experiments. Mycelial growth of the fungus was reduced proportionally with concentrations of 0.1–0.5 ml furfuraldehyde l‐1 agar medium, and viability of sclerotia diminished on exposure to 2‐furfuraldehyde vapours. Detectable populations of bacteria and fungi, including Trichoderma spp., were reduced significantly (9=0.05) when furfuraldehyde was added to the agar used for soil dilution plates of untreated soil. Repeated treatments of natural soil with the fumigant significantly increased populations of Trichoderma spp. and bacteria, but diminished numbers of actinomycetes. Increasing dosages applied to soil artificially infested with S. rolfsii caused a reduction of disease on lentil, Lens culinaris. Results indicate that the compound, when applied to field soil, changes the composition of soil microflora and has potential for integrated control of S. rolfsii. 相似文献
148.
Tracey C. Bourner Enrique Vargas‐Osuna Trevor Williams Candido Santiago‐Alvarez Jenny S. Cory 《Biocontrol Science and Technology》1992,2(4):315-326
Agrotis segetum nuclear polyhedrosis virus (AsNPV) and granulosis virus (AsGV), propagated in laboratory cultures of A. segetum in England and A. ipsilon in Spain, respectively, were applied to plots of maize plants at the one‐ to four‐leaf stage of growth. Plots were arranged in a 6 x 6 Latin square design and infested with second‐instar A. segetum larvae (the common cutworm). Each virus was applied in separate treatments by two application methods; as an aqueous spray containing 0.1% Agral as a wetting agent, and as a bran bait. The NPV was applied at a rate of 4 X 1012 polyhedra/ha, and the GV at 4 X 1013 granules/ha. Soil and plants were sampled for larvae on three occasions following virus treatment: 24 h, 4 days and 11 days. The larvae were reared on diet in the laboratory, until death or pupation, to examine the rate and level of viral infection. Infection data showed 87.5% and 91% NPV infection and 12.5% and 55% GV infection in spray and bait treatments, respectively, in larvae sampled 24 h after treatment. In larvae sampled 4 days after treatment, the results were 78% and 100% NPV infection, and 13% and 6% GV infection. A total of only six larvae were retrieved on day 11. In both treatments larvae infected with AsNPV died significantly more rapidly and at an earlier instar than those infected with AsGV, indicating that AsNPV appears to have better potential as a control agent for A. segetum. 相似文献
149.
150.
前言在我国海涂中被日潮淹没的中、低潮带,天然生长的高等植物种类比较贫乏,分布面积也较小,许多中低潮带海滩为光滩裸地。为了绿化海滩、保护海滩,提高海滩生态系统的初级生产力,我国在1963年和1978年分别从英国 相似文献