全文获取类型
收费全文 | 43626篇 |
免费 | 3090篇 |
国内免费 | 2041篇 |
专业分类
48757篇 |
出版年
2024年 | 95篇 |
2023年 | 797篇 |
2022年 | 1105篇 |
2021年 | 1508篇 |
2020年 | 1448篇 |
2019年 | 1940篇 |
2018年 | 1603篇 |
2017年 | 1092篇 |
2016年 | 1209篇 |
2015年 | 1569篇 |
2014年 | 2389篇 |
2013年 | 3111篇 |
2012年 | 1696篇 |
2011年 | 2163篇 |
2010年 | 1589篇 |
2009年 | 1863篇 |
2008年 | 1881篇 |
2007年 | 1990篇 |
2006年 | 1776篇 |
2005年 | 1691篇 |
2004年 | 1513篇 |
2003年 | 1312篇 |
2002年 | 1301篇 |
2001年 | 1091篇 |
2000年 | 915篇 |
1999年 | 836篇 |
1998年 | 787篇 |
1997年 | 733篇 |
1996年 | 693篇 |
1995年 | 655篇 |
1994年 | 612篇 |
1993年 | 563篇 |
1992年 | 546篇 |
1991年 | 510篇 |
1990年 | 391篇 |
1989年 | 397篇 |
1988年 | 362篇 |
1987年 | 295篇 |
1986年 | 248篇 |
1985年 | 309篇 |
1984年 | 396篇 |
1983年 | 225篇 |
1982年 | 296篇 |
1981年 | 286篇 |
1980年 | 223篇 |
1979年 | 206篇 |
1978年 | 147篇 |
1977年 | 102篇 |
1976年 | 111篇 |
1974年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
981.
George L. Wied Peter H. Bartels Marluce Bibbo May Chen Frank R. Reale Hans Schreiber Jaroslav J. Sychra 《Cell biochemistry and biophysics》1979,1(1):39-54
Cytologic preparations made from the tracheobronchial tree taken by the Schreiber catheter have been scanned by three color
microphotometry. The digitized cell images were processed by the analytical cytodiagnostic programs of the TICAS system. Cells
were sorted into two control groups and five groups of increasing atypia ranging from normal epithelium to invasive squamous
cell carcinoma. Standard statistical tests, including Wilk's Lambda, Rao's V, and the Kruskal-Wallis tests are performed on
these subsets of cell image features. This study demonstrates that discriminant analyses permit differentiation between normal
cells and those from marked atypia or carcinoma and that the classification achieves a high degree of agreement with visual
assignment. 相似文献
982.
The principal characteristics of stomatogenesis during division in Climacostomum virens are: (A) Kinetosomal proliferation on the left side of a variable number of kineties in the ventral somatic cortex forms an oral primordium consisting of several kinetosomal fields, which then fuse to form a single anarchic field. (B) A constant topographical relationship exists between the primordium and a well defined cortical pattern, the zone of discontinuity. (C) The anarchic field primordium divides into 2 unequal parts—to the left, the AZM primordium, and to the right, the paroral primordium, which differentiates into the apical membranelles, the peristomial field, and the buccal tube. (D) Preoral and oblique kineties of the somatic cortex form along the right side of the paroral primordium. (E) Parental oral structures are partially dedifferentiated. Stomatogenesis in C. virens and other heterotrichs is compared. 相似文献
983.
Proliferation and morphology of chick embryo cells cultured in the presence of horse serum and hemoglobin 总被引:2,自引:0,他引:2
Claude Verger 《In vitro cellular & developmental biology. Plant》1979,15(8):587-592
Summary We have shown previously that hemoglobin greatly stimulates chick embryo cell proliferation in Eagle's minimal essential medium
supplemented with horse serum. In the present study we compared the effects of horse serum plus 10 μM hemoglobin to those
of fetal bovine serum on subcultures of chick embryo cells serially propagated at high cell densities. The cells became elongated
in the presence of fetal bovine serum and their rate of proliferation progressively decreased, whereas they became polygonal
in the presence of horse serum plus hemoglobin and proliferated well in successive cell passages. The polygonal cell obtained
in the presence of horse serum plus hemoglobin rapidly elongated if cultured at low cell densities in the presence of fetal
bovine serum, but, in contrast, elongated cells did not yield polygonal cells if cultured at low densities in the presence
of horse serum plus hemoglobin. It is possible that the polygonal and elongated cells are undifferentiated cells and differentiating
myogenic cells, respectively. 相似文献
984.
Lucian J. Cuprak Carol J. Lammi Janet I. Crane 《In vitro cellular & developmental biology. Plant》1979,15(11):900-909
Summary An improved basal medium is presented that requires only minimal supplementation with dialyzed fetal bovine serum or bovine
serum albumin and fetuin to be comparable to Ham's F-10, which requires 15% horse serum (HS) and 2.5% fetal bovine serum (FBS)
for the growth and function of Y-1, mouse adrenal cortex tumor, cells. Cell monolayers maintained for up to 2 weeks without
any protein supplementation have retained their steroid response to ACTH. The medium differs from Ham's F-10 in its buffer
composition and higher calcium-ion concentration. This medium should be a useful adjunct to studies pertaining to steroid
and lipid intermediary metabolism, the retention of a specialized physiological function in a chemically defined medium, and
the mechanism of hormonal response.
Supported by the Medical Research Service of the Veterans Administration. 相似文献
985.
E De Clercq A Billiau V G Edy K L Kirk L A Cohen 《Biochemical and biophysical research communications》1978,82(3):840-846
2-Fluoro-L-Histidine inhibits protein synthesis in various cell cultures, as measured by 3H-leucine incorporation. This histidine analog also inhibits the cytopathogenicity of a number of RNA and DNA viruses in primary and continuous cell cultures; it blocks the transformation of normal mouse (MO) cells by murine sarcoma virus, and partially suppresses the release of murine leukemia virus by a continuously infected mouse cell line (JLSV5). In human skin fibroblasts, it reduces the interferon-inducing capacity of poly(I)·poly(C). Inhibition of cell protein synthesis may be the common cause of the various effects. 4-Fluoro-L-histidine is essentially inert in all of the test systems examined. 相似文献
986.
Evidence is presented for the assignment of the gene for glyoxylase I to mouse chromosome 17 using mouse × Chinese hamster somatic cell hybrids. GLO I was not expressed concordantly with any known marker enzymes which represented 11 linkage groups. The presence of chromosome 17 and expression of GLO I were concordant in 31/31 clones. GLO I is thus linked to the H-2 histocompatibility locus in the mouse. 相似文献
987.
Cercariae of Schistosoma mansoni were treated with undecenyl-pseudothiourea. After centrifugation, they agglutinated into a mass. Resuspended in water, they remained immobilized. When injected sub-cutaneously into mice, they produced bisexual infections. The immobilizing drug effect, together with a reduced worm recovery rate, are time and concentration dependent. The cercariae become avirulent (99.8%) only when the flame cell is affected. Immobilizing and “cercaricidal” effects are not necessarily related properties; the latter can be determined only by in vivo tests of infectivity. No protection against reinfection was noticed in mice injected with immobilized cercariae of reduced virulence. The immobilized cercariae produced infections with a 0.7% worm recovery rate by percutaneous exposure, compared to 2.2% by subcutaneous injection. Normal cercariae produced infections with average recovery rates of 11.1% subcutaneously and 45% percutaneously. 相似文献
988.
989.
Suspension cultures of Perilla ocymoides accumulate caffeic acid, both in free and ester forms, as the only phenylpropanoid end metabolite. Increased levels of growth substances influenced the levels of PAL activity and phenolic accumulation so that cytokinin stimulated, while auxin repressed both parameters. The regulatory role of caffeyl compounds is discussed in relation to their accumulation during the early exponential phase of culture growth. 相似文献
990.
Molecular changes in cell surface membranes resulting from trypsinization of sarcoma 180 tumor cells
John W. Huggins Robert W. Chestnut Norman N. Durham Kermit L. Carraway 《生物化学与生物物理学报:生物膜》1976,426(4):630-637
Sarcoma-180 tumor cells in culture or grown as an ascites form in the CD-1 mouse have been subjected to mild trypsinization procedures in order to study morphological and molecular changes resulting from proteolysis. The cells attached to a substratum become rounded within 20 min and most undergo cell division, but they do not detach from the substratum. Removal of trypsin permits the cells to go back to their original spindle shape over an 8–20 h period.Surface membranes were isolated from trypsinized ascites and cultured cells and subjected to dodecyl sulfate-acrylamide gel electrophoresis. Both cell types showed the same two kinds of changes in electrophoretic patterns. First, there was a loss of glycoproteins from both cell types, even though they show different complements of cell surface glycoproteins. Second, there is a loss of high molecular weight polypeptides, which have previously been suggested to play a role in membrane stabilization and cell shape. These results further implicate these polypeptides in the control of cell morphology and offer circumstantial evidence for transmembrane interactions of surface glycoproteins with the high molecular weight polypeptides as a factor in controlling cell morphology. 相似文献