全文获取类型
收费全文 | 2695篇 |
免费 | 236篇 |
出版年
2023年 | 8篇 |
2022年 | 17篇 |
2021年 | 48篇 |
2020年 | 26篇 |
2019年 | 42篇 |
2018年 | 47篇 |
2017年 | 41篇 |
2016年 | 60篇 |
2015年 | 108篇 |
2014年 | 118篇 |
2013年 | 169篇 |
2012年 | 221篇 |
2011年 | 213篇 |
2010年 | 125篇 |
2009年 | 98篇 |
2008年 | 196篇 |
2007年 | 206篇 |
2006年 | 175篇 |
2005年 | 175篇 |
2004年 | 157篇 |
2003年 | 145篇 |
2002年 | 129篇 |
2001年 | 28篇 |
2000年 | 17篇 |
1999年 | 32篇 |
1998年 | 40篇 |
1997年 | 29篇 |
1996年 | 25篇 |
1995年 | 24篇 |
1994年 | 25篇 |
1993年 | 23篇 |
1992年 | 9篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1971年 | 3篇 |
1962年 | 3篇 |
排序方式: 共有2931条查询结果,搜索用时 390 毫秒
121.
Uzgiris EE Cline H Moasser B Grimmond B Amaratunga M Smith JF Goddard G 《Biomacromolecules》2004,5(1):54-61
The structure of Gd-DTPA-polylysine, Gd-DOTA-polylysine, Gd-SCN-Bz-DOTA-polylysine, and Gd-DTPA-poly(glu:lys) was investigated with circular dichroism, gel permeation chromatography, low angle light scattering, and proton longitudinal relaxivity. Molecular modeling calculations were performed and predicted helical secondary structure for charged Gd-chelator residues, i.e., Gd-DTPA, when the DTPA conjugation levels reached 90% and higher. This helical secondary structure was observed with circular dichroism. The conformational transition from coiled to extended linear was observed also by gel permeation chromatography and by proton relaxivity measurements. The helical secondary structure was not observed when the chelator was changed to DOTA. The residue charge interactions were eliminated in this case since the Gd-DOTA complex had no net charge. For this construct, the gel permeation and relaxivity measurements indicated a coiled conformation. An extended linear conformation was regained when the chelator complex was changed to Gd-SCN-Bz-DOTA, which had a net negative charge. The functional aspects of these structures were investigated by MR imaging of an animal tumor model. The linear extended polymer constructs gave 10-fold higher tumor signals then the coiled-collapsed constructs, indicating a much higher degree of trans-endothelial transport in the tumors. 相似文献
122.
Kemming GI Messick JB Enders G Boros M Lorenz B Muenzing S Kisch-Wedel H Mueller W Hahmann-Mueller A Messmer K Thein E 《Comparative medicine》2004,54(4):404-409
Mycoplasma haemocanis (formerly Haemobartonella canis) is a red blood cell parasite that causes disease mainly in immunosuppressed and splenectomized dogs. Clinical outbreak of the disease resulted in failure of a large experimental project. We aimed to identify whether M. haemocanis has increased prevalence in kennel-raised dogs. In a prospective study, we compared the prevalence of M. haemocanis in whole blood (anti-coagulated by use of EDTA) collected from pet dogs (University of Illinois, Urbana Champaign, Ill.; n = 60) with that in blood from dogs raised in three distinct kennels in western Europe (WE; n = 23), eastern Europe (EE; n = 20), and North America (NA; n = 20). Screening included antibody testing and microscopy of blood smears. The presence of M. haemocanis was identified using a polymerase chain reaction (PCR) assay for specific DNA of the organism. None of the pet dogs (0%) was test positive for M. haemocanis DNA. Mycoplasma haemocanis was found in dogs tested at all of the kennels. Infection rate in the three kennels was 30, 35, and 87%, respectively (all P < 0.001 versus control, chi2-test). Latent infection with M. haemocanis was not a single observation in kennel-raised dogs. Prevalence may be higher than that in a pet dog population. The potential exists for these latent infections to adversely affect or confound research results. 相似文献
123.
El Mohsen MA Marks J Kuhnle G Rice-Evans C Moore K Gibson G Debnam E Srai SK 《Free radical research》2004,38(12):1329-1340
Citrus flavonoids have been investigated for their biological activity, with both anti-inflammatory and -carcinogenic effects being reported. However, little information is known on the bioavailability of these compounds in vivo. The objectives of this study were to determine the tissue distribution of naringenin after gastric gavage of [3H]-naringenin to rats. Unlabelled naringenin was also used to quantify the levels of naringenin and its major metabolites in tissues and eliminated in the urine and faeces. Significant radioactivity was detected in the plasma as well as all tissues examined 2 h post-gavage. After 18 h, higher levels of radioactivity were retained in plasma and tissues (55% of the administered radioactivity). Investigation of the nature of metabolites, using unlabelled naringenin, revealed that the glucuronides were the major components in plasma, tissues and urine, in addition to the colonic metabolite 3-(4-hydroxyphenyl) propionic acid, detected in the urine. The aglycone was the form extensively retained in tissues after 18 h post-gavage. Total identified metabolites detected after 18 h in most tissues were only 1-5% of the levels detected after 2 h. However, the brain, lungs and heart retained 27, 20 and 11%, respectively, relative to the total metabolites detected at 2 h. While radioactive detection suggests increased levels of breakdown products of naringenin after 18 h versus 2 h, the products identified using unlabelled naringenin are not consistent with this, suggesting that a predominant proportion of the naringenin breakdown products at 18 h are retained as smaller decomposition molecules which cannot yet be identified. 相似文献
124.
A microarray-based high throughput molecular marker genotyping method: the tagged microarray marker (TAM) approach 总被引:6,自引:0,他引:6
Flavell AJ Bolshakov VN Booth A Jing R Russell J Ellis TH Isaac P 《Nucleic acids research》2003,31(19):e115
A microarray-based method has been developed for scoring thousands of DNAs for a co-dominant molecular marker on a glass slide. The approach was developed to detect insertional polymorphism of transposons and works well with single nucleotide polymorphism (SNP) markers. Biotin- terminated allele-specific PCR products are spotted unpurified onto streptavidin-coated glass slides and visualised by hybridisation of fluorescent detector oligonucleotides to tags attached to the allele- specific PCR primers. Two tagged primer oligonucleotides are used per locus and each tag is detected by hybridisation to a concatameric DNA probe labelled with multiple fluorochromes. 相似文献
125.
126.
Lariguet P Boccalandro HE Alonso JM Ecker JR Chory J Casal JJ Fankhauser C 《The Plant cell》2003,15(12):2966-2978
Phytochrome kinase substrate1 (PKS1) is a cytoplasmic protein that interacts physically with, and is phosphorylated by, the plant photoreceptor phytochrome. Here, we show that light transiently increases PKS1 mRNA levels and concentrates its expression to the elongation zone of the hypocotyl and root. This response is mediated by phytochrome A (phyA) acting in the very low fluence response (VLFR) mode. In the hypocotyl, PKS1 RNA and protein accumulation are maintained only under prolonged incubation in far-red light, the wavelength that most effectively activates phyA. Null mutants of PKS1 and its closest homolog, PKS2, show enhanced phyA-mediated VLFR. Notably, a pks1 pks2 double mutant has no phenotype, whereas overexpression of either PKS1 or PKS2 results in the same phenotype as the pks1 or pks2 single null mutant. We propose that PKS1 and PKS2 are involved in a growth regulatory loop that provides homeostasis to phyA signaling in the VLFR. In accordance with this idea, PKS1 effects are larger in the pks2 background (and vice versa). Moreover, the two proteins can interact with each other, and PKS2 negatively regulates PKS1 protein levels specifically under VLFR conditions. 相似文献
127.
Mo RR Eisenbraun JK Sonstein J Craig RA Curtis JL Stoolman LM Chen J Yung RL 《Journal of immunology (Baltimore, Md. : 1950)》2003,171(2):745-753
D10.G4.1 (D10) cells, a murine conalbumin-reactive Th2 cell line, made to overexpress the beta(2) integrin LFA-1 by pharmacological manipulation or by transfection become autoreactive and are capable of inducing in vivo autoimmunity. However, whether this is specific to LFA-1 and whether overexpression of other T cell integrin molecules has the same effect are unknown. We examined the functional consequences of T cell CD49d (alpha(4) integrin) overexpression by transfecting murine CD49d cDNA into D10 cells. Similar to the LFA-1-transfected cells, the CD49d-overexpressing T cells are autoreactive and proliferate in response to APCs in an MHC class II-dependent manner in the absence of nominal Ag. Additionally, CD49d overexpression is associated with increased in vitro adhesion to endothelial cells and increased in vivo splenic homing. However, in contrast to LFA-1 overexpression, increased T cell CD49d expression is not associated with autoreactive cytotoxicity or the ability to induce in vivo autoimmunity. In addition to the novel observation that CD49d overexpression is sufficient to induce T cell autoreactivity, our results also support the hypothesis that the ability to induce in vivo autoimmunity is related to T cell cytotoxicity and not to T cell proliferation function in the D10 murine adoptive transfer model of autoimmunity. 相似文献
128.
129.
Either of the CD45RB and CD45RO isoforms are effective in restoring T cell,but not B cell,development and function in CD45-null mice 总被引:4,自引:0,他引:4
Ogilvy S Louis-Dit-Sully C Cooper J Cassady RL Alexander DR Holmes N 《Journal of immunology (Baltimore, Md. : 1950)》2003,171(4):1792-1800
The protein tyrosine phosphatase CD45 is expressed as a series of isoforms whose tissue and differentiation stage specificity is broadly conserved in evolution. CD45 has been shown to be an important regulator of a variety of functions in many different hemopoietic lineages. We have chosen an in vivo genetic complementation strategy to investigate the differential functions between isoforms. In this study, we report the characterization of transgenic mice which express the isoforms CD45RO or CD45RB as their only CD45 molecules, at a variety of expression levels and in the majority of hemopoietic lineages. Both CD45RO and CD45RB isoforms reconstitute thymocyte development in a CD45-null mouse background when expressed above a threshold level. The resulting mature T cells populate the peripheral lymphoid organs where they are found at normal frequency. Both CD45RO and CD45RB isoforms also permit T cell function in the periphery, although the threshold for normal function here appears to be set higher than in the thymus. In contrast, neither isoform is capable of fully restoring peripheral B cell maturation, even at levels approaching those in heterozygous CD45(+/-) mice in which maturation is normal. In vitro activation of B cells by Ag-receptor stimulation is only minimally complemented by these CD45RO and CD45RB transgenes. Our results suggest that CD45 isoforms play unique roles which differ between the T and B lineages. 相似文献
130.
Trubey CM Chertova E Coren LV Hilburn JM Hixson CV Nagashima K Lifson JD Ott DE 《Journal of virology》2003,77(23):12699-12709
Among the many host cell-derived proteins found in human immunodeficiency virus type 1 (HIV-1), HLA class II (HLA-II) appears to be selectively incorporated onto virions and may contribute to mechanisms of indirect imunopathogenesis in HIV infection and AIDS. However, the amount of HLA-II on the surface of HIV-1 particles has not been reliably determined due to contamination of virus preparations by microvesicles containing host cell proteins, including HLA-II. Even rigorous sucrose density centrifugation is unable to completely separate HIV-1 from microvesicles. CD45, a leukocyte integral membrane protein, is found on microvesicles, yet appears to be excluded from HIV-1 particles. Exploiting this observation, we have developed a CD45-based immunoaffinity depletion method for removing CD45-containing microvesicles that yields highly purified preparations of virions. Examination of CD45-depleted HIV-1(MN) by high-pressure liquid chromatography, protein sequencing, and amino acid analyses determined a molar ratio of HLA-II to Gag of 0.04 to 0.05 in the purified virions, corresponding to an estimated average of 50 to 63 native HLA-II complexes (i.e., a dimer of alpha and beta heterodimers) per virion. These values are approximately 5- to 10-fold lower than those previously determined for other virion preparations that contained microvesicles. Our observations demonstrate the utility of CD45 immunoaffinity-based approaches for producing highly purified retrovirus preparations for applications that would benefit from the use of virus that is essentially free of microvesicles. 相似文献