全文获取类型
收费全文 | 773篇 |
免费 | 148篇 |
国内免费 | 3篇 |
专业分类
924篇 |
出版年
2022年 | 6篇 |
2020年 | 6篇 |
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 9篇 |
2015年 | 30篇 |
2014年 | 23篇 |
2013年 | 39篇 |
2012年 | 55篇 |
2011年 | 55篇 |
2010年 | 33篇 |
2009年 | 27篇 |
2008年 | 33篇 |
2007年 | 27篇 |
2006年 | 25篇 |
2005年 | 24篇 |
2004年 | 26篇 |
2003年 | 25篇 |
2002年 | 22篇 |
2001年 | 24篇 |
2000年 | 26篇 |
1999年 | 22篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 14篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 29篇 |
1991年 | 19篇 |
1990年 | 21篇 |
1989年 | 18篇 |
1988年 | 16篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 18篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 15篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1976年 | 15篇 |
1975年 | 8篇 |
1974年 | 9篇 |
1973年 | 5篇 |
1972年 | 6篇 |
1971年 | 7篇 |
排序方式: 共有924条查询结果,搜索用时 15 毫秒
101.
NFIL3 Suppresses Hypoxia‐induced Apoptotic Cell Death by Targeting the Insulin‐like Growth Factor 2 Receptor 下载免费PDF全文
102.
Ni-Fe containing enzymes are involved in the biological utilization of carbon monoxide, carbon dioxide, and hydrogen. Interest in these enzymes has increased in recent years due to hydrogen fuel initiatives and concerns over development of new methods for CO2 sequestration. One Ni-Fe enzyme called carbon monoxide dehydrogenase (CODH) is a key player in the global carbon cycle and carries out the interconversion of the environmental pollutant CO and the greenhouse gas CO2. The Ni-Fe center responsible for this important chemistry, the C-cluster, has been the source of much controversy, but several recent structural studies have helped to direct the field toward a unifying mechanism. Here we summarize the current state of understanding of this fascinating metallocluster. 相似文献
103.
Background
Elevated glucose-regulated protein 78 (GRP78) levels in tissues have been known to be related with poor prognosis in hepatocellular carcinoma (HCC) patients. Though the variants in the 3′ untranslated region (UTR) of GRP78 gene were not associated with HCC risk, we wonder whether these polymorphisms affect survival of HCC patients.Methodology/Principal Findings
Blood samples of HCC patients were maintained in our specimen bank between 1996 to 2003. DNA from 576 unrelated and resectable patients with HCC was typed for rs16927997 (T>C), rs1140763 (T>C) and rs12009 (T>C) by TaqMan assays. The Kaplan-Meier method and log-rank test were used to estimate overall survival. Linkage disequilibrium (LD) analysis identified a total of 3 haplotypes and 6 diplotypes in this region. The distribution of haplotype was not related to the clinical characteristics. Univariate analysis showed that the allele, genotype, haplotype and diplotype did not effect the survival. None of the clinical features show a significant association (P correced>0.05) with overall patient outcome in multiple comparisons.Conclusions/Significance
There is no noteworthy influence of 3′ UTR variants in the GRP78 on prognosis of resectable HCC in the Chinese population. 相似文献104.
M Buechner A H Delcour B Martinac J Adler C Kung 《Biochimica et biophysica acta》1990,1024(1):111-121
The electrical properties of Escherichia coli cells were examined by the patch-clamp technique. Giant cells or giant spheroplasts were generated by five different methods. By electron micrographic and other criteria we determined that the patches are most likely from the outer membrane. We regularly observed currents through at least two types of channels in this membrane. The first current is mechanosensitive and voltage-dependent, and can be observed in single gene mutants of the known major porins (ompF, ompC, phoE, lamB); this channel may represent a minor porin or a new class of outer membrane protein. The possible identity of the second, voltage-sensitive channel with one of the known outer membrane proteins is being explored. The high-resistance seals consistently formed on these patches and the presence of gated ion channels suggest that most of the pores of the outer membrane are not statically open, as commonly held, but are closed at rest and may be openable by physiological stimuli. 相似文献
105.
Kung‐Jong Lui Xiao‐Hua Zhou Chii‐Dean Lin 《Biometrical journal. Biometrische Zeitschrift》2004,46(6):642-652
When a new diagnostic procedure is developed, it is important to assess whether the diagnostic accuracy of the new procedure is different from that of the standard procedure. For paired‐sample ordinal data, this paper develops two test statistics for testing equality of the diagnostic accuracy between two procedures without assuming any parametric models. One is derived on the basis of the probability of correctly identifying the case for a randomly selected pair of a case and a non‐case over all possible cutoff points, and the other is derived on the basis of the sensitivity and specificity directly. To illustrate the practical use of the proposed test procedures, this paper includes an example regarding the use of digitized and plain films for screening breast cancer. This paper also applies Monte Carlo simulation to evaluate the finite sample performance of the two statistics developed here and notes that they can perform well in a variety of situations. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
106.
Efficient and seamless DNA recombineering using a thymidylate synthase A selection system in Escherichia coli 总被引:3,自引:1,他引:2 下载免费PDF全文
λ-Red system-based recombinogenic engineering is a powerful new method to engineer DNA without the need for restriction enzymes or ligases. Here, we report the use of a single selectable marker to enhance the usefulness of this approach. The strategy is to utilize the thymidylate synthase A (thyA) gene, which encodes an enzyme involved in the synthesis of thymidine 5′-triphosphate, for both positive and negative selection. With this approach, we successfully created point mutations in plasmid and bacterial artificial chromosome (BAC) DNA containing the mouse Col10a1 gene. The results showed that the thyA selection system is highly efficient and accurate, giving an average of >90% selection efficiency. This selection system produces DNA that is free from permanent integration of unwanted sequences, thus allowing unlimited rounds of modifications if required. 相似文献
107.
108.
Bi-directional regulation between tyrosine kinase Etk/BMX and tumor suppressor p53 in response to DNA damage 总被引:3,自引:0,他引:3
109.
Virus persistence in an animal model of multiple sclerosis requires virion attachment to sialic acid coreceptors 下载免费PDF全文
Persistent Theiler's virus infection in the central nervous system (CNS) of mice provides a highly relevant animal model for multiple sclerosis. The low-neurovirulence DA strain uses sialic acid as a coreceptor for cell binding before establishing infection. During adaptation of DA virus to growth in sialic acid-deficient cells, three amino acid substitutions (G1100D, T1081I, and T3182A) in the capsid arose, and the virus no longer used sialic acid as a coreceptor. The adapted virus retained acute CNS virulence, but its persistence in the CNS, white matter inflammation, and demyelination were largely abrogated. Infection of murine macrophage but not oligodendrocyte cultures with the adapted virus was also significantly reduced. Substitution of G1100D in an infectious DA virus cDNA clone demonstrated a major role for this mutation in loss of sialic acid binding and CNS persistence. These data indicate a direct role for sialic acid binding in Theiler's murine encephalomyelitis virus persistence and chronic demyelinating disease. 相似文献
110.
Marek's disease virus-encoded vIL-8 gene is involved in early cytolytic infection but dispensable for establishment of latency 总被引:3,自引:0,他引:3 下载免费PDF全文
Marek's disease, a lymphoproliferative disease of chickens, is caused by an alphaherpesvirus, Marek's disease virus (MDV). This virus encodes a virokine, vIL-8, with general homology to cellular CXC chemokines such as interleukin-8 (IL-8) and Gro-alpha. To study the function of vIL-8 gene, we deleted both copies of vIL-8 residing in the terminal repeat long and internal repeat long region of the viral genome and generated a mutant virus with vIL-8 deleted, rMd5/DeltavIL-8. Growth kinetics study showed that vIL-8 gene is dispensable for virus replication in cell culture. In vivo, the vIL-8 gene is involved in early cytolytic infections in lymphoid organs, as evidenced by limited viral antigen expression of rMd5/DeltavIL-8. However, the rMd5/DeltavIL-8 virus is unimpaired in virus replication in the feather follicle epithelium. vIL-8 does not appear to be important for establishment of latency, since rMd5/DeltavIL-8 and the wild-type virus have similar viremia titers at 14 days postinfection, a period when the virus titer comes primarily from reactivated latent genomes. Nevertheless, because of the impaired cytolytic infections, the overall transformation efficiency of the virus with vIL-8 deleted is much lower, as reflected by the reduced number of transformed cells at 5 weeks postinoculation and the presence of fewer gross tumors. Importantly, the revertant virus that restored the expression of vIL-8 gene also restored the wild-type phenotype, indicating the deficient phenotypes are results of vIL-8 deletion. One of the interesting differences between the MDV vIL-8 gene and its cellular counterpart is the presence of a DKR (Asp-Lys-Arg) motif instead of ELR (Glu-Leu-Arg) preceding the invariable CXC motif. To study the significance of this variation, we generated recombinant MDV, rMd5/vIL-8-ELR, carrying the ELR motif. Both in vitro and in vivo studies revealed that the DKR motif is as competent as ELR in pathogenesis of MDV. 相似文献