全文获取类型
收费全文 | 10850篇 |
免费 | 563篇 |
国内免费 | 4篇 |
出版年
2022年 | 58篇 |
2021年 | 116篇 |
2020年 | 60篇 |
2019年 | 83篇 |
2018年 | 121篇 |
2017年 | 112篇 |
2016年 | 163篇 |
2015年 | 257篇 |
2014年 | 307篇 |
2013年 | 638篇 |
2012年 | 550篇 |
2011年 | 487篇 |
2010年 | 319篇 |
2009年 | 317篇 |
2008年 | 518篇 |
2007年 | 490篇 |
2006年 | 501篇 |
2005年 | 465篇 |
2004年 | 456篇 |
2003年 | 468篇 |
2002年 | 413篇 |
2001年 | 417篇 |
2000年 | 412篇 |
1999年 | 340篇 |
1998年 | 147篇 |
1997年 | 116篇 |
1996年 | 86篇 |
1995年 | 90篇 |
1994年 | 88篇 |
1993年 | 92篇 |
1992年 | 251篇 |
1991年 | 250篇 |
1990年 | 200篇 |
1989年 | 186篇 |
1988年 | 188篇 |
1987年 | 162篇 |
1986年 | 149篇 |
1985年 | 148篇 |
1984年 | 122篇 |
1983年 | 110篇 |
1982年 | 93篇 |
1981年 | 59篇 |
1980年 | 63篇 |
1979年 | 90篇 |
1978年 | 85篇 |
1977年 | 61篇 |
1976年 | 59篇 |
1975年 | 49篇 |
1973年 | 58篇 |
1970年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Kiyoshi Takahashi Katsuya Miyatani Hiroyuki Yanai Ho Jong Jeon Kotaro Fujiwara Tadashi Yoshino Kazuhiko Hayashi Tadaatsu Akagi Ken Tsutsui Koichi Mizobuchi 《Virchows Archiv. B, Cell pathology including molecular pathology》1992,62(1):105-113
Monocytic leukemia (MoL) cells were obtained from the peripheral blood of a patient in whom the leukemic cells infiltrating
various lymphoreticular organs exhibited features intermediate between interdigitating reticulum cells (IDC) and ordinary
phagocytic macrophages, whereas the leukemic cells in the peripheral blood were essentially monocytic and lacked such features.
Peripheral blood CD4+ T-cells were established as an interleukin-2-dependent T-cell line. When the MoL cells were exposed
for a few days to conditioned medium from the T-cell line, they extended several dendritic cytoplasmic projections and became
intensely positive for HLA-DR antigen, cytoplasmic S-100β protein, and CD1 antigen. Functionally, the conditioned medium significantly
down-regulated Fc-mediated and Fc-independent phagocytic activities, and the levels of lysosomal enzymes such as lysozyme
and nonspecific esterase in the MoL cells. Moreover, the conditioned medium significantly up-regulated the accessory cell
function of the MoL cells as measured by the primary allogenic mixed leukocyte reaction (MLR). Furthermore, the conditioned
medium significantly down-regulated the expression of CD14 antigen.
Biochemical analysis indicated that the factor responsible for these changes is a protein which is distinct from known human
cytokines and whose molecular weight is approximately 31 kDa. These findings suggest that IDC are closely related the monocytic
lineage and that helper T-cells play an important role in constructing the microenvironment of T-lymphoid tissues which is
necessary for the differentiation and maturation of IDC. 相似文献
92.
Immunotargeting of daunomycin to localized and metastatic human colon adenocarcinoma in athymic mice
Esther Hurwitz Ruth Adler Daniel Shouval Hiroshi Takahashi Jack R. Wands Michael Sela 《Cancer immunology, immunotherapy : CII》1992,35(3):186-192
Summary A monoclonal antibody (designated SF25), which recognizes a protein antigen expressed on a large number of human colon carcinomas, was used for drug targeting. Daunomycin-antibody conjugates were prepared by two previously described procedures. In one, the drug was bound to the antibody through a spacer of small molecular mass (cis-aconitic acid), while in the other a dextran bridge served as the link between drug and antibody. High substitution rates of drug to antibody were obtained using the latter binding procedure. Both conjugates were tested in vitro against two human colon carcinoma cell lines, LS180 and KM-12. The efficacy of a daunomycin-dextran-SF25 antibody conjugate was tested against colon carcinoma LS180 tumors transplanted at different sites into athymic mice. The specific conjugate was significantly more inhibitory to a subcutaneous tumor growth than its components or their mixture. SF25 antibody alone showed antitumoral effects against all three forms of transplanted tumor tested, namely, local, metastatic or intrahepatic, whereas daunomycin, on its own, was effective only against the subcutaneous tumor. Binding of daunomycin to dextran partially improved its inhibitory activity against the metastatic tumor. The conjugate, daunomycin-dextran-SF25 antibody reduced the number of metastatic foci, increased the survival rate and delayed death. Yet against lymph node metastases it was not significantly better than a mixture of both constituents. However, results obtained with an intrahepatic tumor, a model that mimics the natural progression of the disease, resembled those described with the subcutaneous tumor. Daunomycin-dextran-SF25 antibody was significantly more effective than all components separately and than a mixture of drug and antibody, provided a highly drug-substituted conjugate was used. 相似文献
93.
To obtain new RFLP markers for construction of a high-resolution map of human chromosome 8, a cosmid library was constructed from a somatic hybrid cell that contained chromosome 8 as the only human component in mouse genomic background. Eighty-eight new RFLP markers were isolated and characterized, and 71 of them were sublocalized to chromosomal bands by fluorescent in situ hybridization (FISH). Of these, 36 were localized to the short arm, 34 to the long arm, and 1 to the centromeric region. Five markers defined VNTR loci. This work represents the first extensive isolation and physical mapping of RFLP markers on human chromosome 8. These new markers will serve as useful resources for linkage mapping of loci for inherited diseases and for efforts to identify a putative tumor suppressor gene(s) on chromosome 8. 相似文献
94.
Cellular targets and trophic functions of neurotrophin-3 in the developing rat hippocampus. 总被引:13,自引:0,他引:13
The expression of the neurotrophins and trk receptors in the hippocampus has directed attention toward their roles in the development and maintenance of this region. We have examined the effects of the neurotrophins NT-3, BDNF, and NGF in cultures of developing rat hippocampal cells by two criteria: rapid induction of c-fos and neurotrophic responses. The selective induction of c-fos mRNA suggests the presence of functional receptors for NT-3 and BDNF, but not NGF, in embryonic hippocampal cultures. The NT-3-responsive cells were localized in pyramidal neurons of areas CA1 through CA3 and dentate granular and hilar cells of postnatal organotypic slices, as detected by c-Fos immunocytochemistry. In addition to immediate early responses, NT-3 caused a 10-fold increase in the number of cells expressing the neuronal antigen calbindin-D28k. This increase was dose dependent, with maximal stimulation at 10 ng/ml. In contrast, BDNF elicited small but significant calbindin responses. These results indicate biological responses to NT-3 in the CNS and suggest roles for for this neurotrophin during hippocampal neurogenesis. 相似文献
95.
The amount of 22- and 23-kDa polypeptides in a 23-kDa protein family, which plays a regulatory role in photosynthetic oxygen evolution, decreased significantly during the progress of appearance of chlorotic spots in cucumber mosaic virus strain Y (CMV[Y])-inoculated tobacco (Nicotiana tabacum 'Ky57') leaves (Plant Mol. Biol. 16:689-698, 1991). The present study was conducted to determine if the amount of other polypeptides of the oxygen-evolving complex and the oxygen-evolving activity also decreased in CMV(Y)-inoculated tobacco leaves. The amount of a 33-kDa polypeptide, which is essential to oxygen evolution, did not decrease in CMV(Y)-inoculated leaves showing early symptoms, although the amount of 22- and 23-kDa polypeptides began to decrease. However, comparative analysis of electron transport in thylakoid membranes indicated that the oxygen-evolving activity in CMV(Y)-inoculated tobacco leaves was only partly reduced, compared with the activity in CMV(O)-inoculated tobacco leaves which did not show clear symptoms. Partial inhibition of the oxygen-evolving activity, by a differential decrease in the amount of polypeptides of the oxygen-evolving complex, seems to be associated with the primary molecular process of symptom expression in CMV(Y)-inoculated tobacco leaves. 相似文献
96.
Kenji Kato Su-wan Oh Hiroyuki Yamamoto Takayuki Hanazato Ikuko Yasuda Akira Otuki Masayuki Takahashi 《Ecological Research》1992,7(3):267-276
In order to understand the control mechanisms of a large, stable bacterial standing stock, enclosure experiments were conducted
in a eutrophic lake, where both bacterial productivity and grazing pressure were very high. Total bacterial number in the
different enclosures ranged from 1.2 to 2.7×107 cells mL−1 throughout the experiment. The average bacterial cell production rate estimated from a grazer eliminating experiment was
6.3×105 cells mL−1 h−1. Difference in the bacterial cell production rate between shaded and unshaded enclosures was not apparent. Bacteria showed
a reduction in standing stock of only about 25–30% even after the supply of light was cut to 1%. Bacteria in the shaded enclosures
then recovered their production rate in the first 12 days of perturbation. Grazing pressure in the shaded enclosures was not
less than that for the control. Thus, it was considered a control mechanism of bacterial stable standing stock that the bacteria
shifted their organic substrate from extracellular dissolved organic carbon freshly released from phytoplankton to that already
stocked in the water column, though it is not known whether the dominant bacteria were the same. 相似文献
97.
Multiple rpoD-related genes of cyanobacteria. 总被引:3,自引:0,他引:3
Genomes of many eubacterial strains have been shown to encode for multiple rpoD-related genes. In this report, we describe the identification of the multiple rpoD-related genes of cyanobacterial strains. DNAs of three cyanobacterial strains, Anabaena sp. PCC7120, Synechococcus sp. PCC7942, and Synechocystis sp. PCC6803, were examined by Southern hybridization, using a synthetic probe designed for detecting rpoD or rpoD-related genes. Four or five hybridization signals were found in each DNA. Four DNA regions of Synechococcus sp. PCC7942 corresponding to the hybridization signals were cloned and partially sequenced. The sequence data indicate the presence of genes, named rpoD1, rpoD2, rpoD3, and rpoD4, whose products are highly similar to the basic structure of the principal sigma factors of eubacterial strains. The rpoD1 gene showed the greatest similarity to the sigA gene of Anabaena sp. PCC7120. 相似文献
98.
Setsuzo Tada Katsuya Gomi Katsuhiko Kitamoto Kojiro Takahashi Gakuzo Tamura Shodo Hara 《Molecular & general genetics : MGG》1991,229(2):301-306
Summary Northern blot analysis of glucose-grown and starch-grown mycelia of Aspergillus oryzae R11340 was conducted using the cloned Taka-amylase A (TAA) gene as a probe. The amount of mRNA homologous to the TAA gene was increased when this fungus was grown with starch as a sole carbon source. In order to analyze the induction mechanism, we inserted the Escherichia coli uidA gene encoding -glucuronidase (GUS) downstream of the TAA promoter and introduced the resultant fusion gene into the A. oryzae genome. Production of a functional GUS protein was induced by starch, but not by glucose. When the effects of various sugars on expression of the fusion gene were examined, the results suggested that the expression of the fusion gene was under control of the TAA gene promoter. 相似文献
99.
Root hydrotropism of an agravitropic pea mutant, ageotropum 总被引:3,自引:0,他引:3
We have partially characterized root hydrotropism of an agravitropic pea mutant, ageotropum (from Pisum sativum L. cv. Weibull's Weitor), without interference of gravitropism. Lowering the atmospheric air humidity inhibited root elongation and caused root curvature toward the moisture-saturated substrate in ageotropum pea. Removal of root tips approximately 1.5 mm in length blocked the hydrotropic response. A computer-assisted image analysis showed that the hydrotropic curvature in the roots of ageotropum pea was chiefly due to a greater inhibition of elongation on the humid side than the dry side of the roots. Similarly, gravitropic curvature of Alaska pea roots resulted from inhibition of elongation on the lower side of the horizontally placed roots, while the upper side of the roots maintained a normal growth rate. Gravitropic bending of Alaska pea roots was apparent 30 min after stimulation, whereas differential growth as well as curvature in positive root hydrotropism of ageotropum pea became visible 4–5 h after the continuous hydrostimulation. Application of 2,3,5-triiodobenzoic acid or ethyleneglycol-bis-( β -aminoethylether)-N,N,N',N'-tetraacetic acid was inhibitory to both root hydrotropism of ageotropum pea and root gravitropism of Alaska pea. Some mutual response mechanism for both hydrotropism and gravitropism may exist in roots, although the stimulusperception mechanisms differ from one another. 相似文献
100.
Fujita Yuichi; Takahashi Yasuhiro; Shonai Fumio; Ogura Yutaka; Matsubara Hiroshi 《Plant & cell physiology》1991,32(7):1093-1106
The frxC gene, found in liverwort chloroplast DNA, encodes aprotein of unknown function. The deduced amino acid sequenceof the protein shows significant homology to that of ni-trogenaseFe-protein encoded by the nifH gene. We have cloned the frxCand nifH genes from the nitrogen-fixing cyanobacterium Plectonemaboryanum, using frxC- and nifH-specific probes, and have determinedtheir nucleotide sequences. The amino acid sequence deducedfrom the frxC gene of P. boryanum exhibits 83% homology to thatof the protein encoded by the/rxCgene from liverwort, whereasit exhibits only 34% homology to that encoded by the nifH genefrom the same organism, namely, P. boryanum. Northern blot analysisshowed that the frxC gene was transcribed more actively undernitrogenase-repressed conditions than under nitrogenase-inducedconditions, suggesting that the FrxC protein has a functiondistinct from nitrogen fixation. These results, together withthe phylogenetic relationship between the nifH and frxC genes,indicate that the frxC and nifH genes are derived from a commonancestral gene but have evolved independently to encode proteinswith different functions. (Received April 27, 1991; Accepted August 12, 1991) 相似文献