全文获取类型
收费全文 | 4726篇 |
免费 | 237篇 |
国内免费 | 409篇 |
出版年
2023年 | 52篇 |
2022年 | 75篇 |
2021年 | 100篇 |
2020年 | 97篇 |
2019年 | 130篇 |
2018年 | 131篇 |
2017年 | 94篇 |
2016年 | 101篇 |
2015年 | 136篇 |
2014年 | 280篇 |
2013年 | 287篇 |
2012年 | 231篇 |
2011年 | 302篇 |
2010年 | 221篇 |
2009年 | 238篇 |
2008年 | 255篇 |
2007年 | 321篇 |
2006年 | 230篇 |
2005年 | 187篇 |
2004年 | 146篇 |
2003年 | 135篇 |
2002年 | 118篇 |
2001年 | 102篇 |
2000年 | 86篇 |
1999年 | 107篇 |
1998年 | 72篇 |
1997年 | 71篇 |
1996年 | 67篇 |
1995年 | 68篇 |
1994年 | 54篇 |
1993年 | 62篇 |
1992年 | 65篇 |
1991年 | 64篇 |
1990年 | 48篇 |
1989年 | 37篇 |
1988年 | 32篇 |
1987年 | 49篇 |
1986年 | 24篇 |
1985年 | 63篇 |
1984年 | 53篇 |
1983年 | 49篇 |
1982年 | 39篇 |
1981年 | 37篇 |
1980年 | 49篇 |
1979年 | 33篇 |
1978年 | 37篇 |
1977年 | 25篇 |
1976年 | 29篇 |
1975年 | 25篇 |
1973年 | 21篇 |
排序方式: 共有5372条查询结果,搜索用时 15 毫秒
11.
I. A. Catalán † E. Berdalet † M. P. Olivar † C. Roldán † 《Journal of fish biology》2007,70(2):391-405
Six condition indices based on RNA, total soluble protein and two metabolic enzymes [lactate dehydrogenase (LDH) and citrate synthase (CS)] were analysed in muscle tissue of individual larvae, post-flexion reared sea bass Dicentrarchus labrax using DNA and total soluble protein as standards for size. In addition, the effect of 2 days of food deprivation on the cell proliferation rates was assessed. The RNA:DNA best reflected short-term changes in feeding conditions. If standardized by DNA content, LDH activity was a better indicator of condition than any other index but RNA:DNA. Further, the analysis of cell proliferation rates in muscle from 26 day-old larvae proved useful in distinguishing continuously fed larvae from individuals subjected to 2 days of fast. 相似文献
12.
Growth on culture media results in changes in Rhizobium competitivity:Bradyrhizobium japonicum strain G2, when mixed with the strain GMB 1 in the same ratio, formed 85% of the total nodule numbers when the strains were
cultured on the YEM medium, whereas, it formed only 55% of the nodules when they were cultured on the MSY medium. 相似文献
13.
14.
小麦—天兰偃麦草—黑麦三属杂种花粉植株诱导条件的研究 总被引:3,自引:1,他引:2
研究表明,三属杂种处于单核中晚期阶段的花粉最适于诱导形成愈伤组织。低温预处理对促进三属杂种花粉愈伤组织的诱导有一定的作用。利用以马铃薯提取物为基础物质的马铃薯-Ⅱ培养基作诱导培养基,其愈伤组织诱导与分化的频率比目前两个较好的合成培养基要高。同一个三属杂种F_1春、秋播种植株之间在形成愈伤组织的能力上有较大的差异,秋播材料形成愈伤组织的能力明显高于春播材料。F_(?)杂种植株诱导愈伤组织和分化植株的频率均比F_1杂种明显提高。 相似文献
15.
Valerio Vidotto Giuseppe Picerno Stefano Caramello Giovanna Paniate 《Mycopathologia》1988,104(3):129-135
The passage between the yeast and mycelial forms of Candida albicans B 311-10 was studied by using the minimal syntehtic medium of Shepherd et al. [19] modified without biotin and with low glucose concentrations. It was observed that biotin, aminoacids and particularly pH are not important factors in the dimorphism of C. albicans. The only factor of notable importance in the passage of yeast form to mycelial form in C. albicans was glucose concentration. 相似文献
16.
Egg yolk lipoprotein promoted growth of a wide variety of mammalian cell lines, including plasma-cytomas and epithelial cell lines, in serum-free medium. The lipoprotein was active for cell growth when used with insulin, transferrin, ethanolamine and selenite. The most active lipoprotein fraction (YLP-pI7.5) was purified to give a single peak by chromatofocusing and gel filtration, and was homogeneous on a 0.35% agarose gel electrophoretogram. The lipoprotein was characterised as a very low density lipoprotein with a protein content of only 1.3%. This lipoprotein had an optimal concentration of 300 g/ml (4 g protein/ml). It was easily separable from proteinous molecules secreted into the serum-free medium by the cells, since it floated on the surface of the medium after addition of ammonium sulfate, to precipitate protein, and centrifugation. An associated structure of lipid and protein seemed to be still necessary for the lipoprotein to exhibit a growth promoting activity. 相似文献
17.
A serum free medium was developed, that could be used for the large scale propagation of various cell lines in bioreactors. The medium is based on a 1:1 mixture of Iscove's Modified Dulbecco's Medium and Ham's Medium F12, supplemented with transferrin, insulin and a BSA/oleic acid complex. Several myelomas, hybridomas derived from different myelomas and spleen cells, and other lymphoid and non-lymphoid cell lines were cultivated at growth rates comparable to those observed using serum-supplemented media. There was furthermore no reduction in the formation of products such as monoclonal antibodies or recombinant human interleukin-2.Abbreviations Ag8
Mouse myeloma cell line P3-X63-Ag8.653
- BME
Basal Medium Eagle
- BSA
Bovine Serum Albumin
- DMEM
Dulbecco's Modified Eagle's Medium
- EDTA
Ethylenediaminete-traacetic Acid
- e-PC
Phosphatidyl choline from egg yolk
- FCS
Fetal Calf Serum
- FGF
Fibroblast Growth Factor
- GHL
Glycyl-histidyl-lysine
- HDL
High Density Lipoprotein
- HPL
Human Plasma Lipid
- IF
1:1 mixture of IMDM and Ham's F12
- IMDM
Iscove's Modified Dulbecco's medium
- LDL
Low Density Lipoprotein
- NS1
Mouse myeloma cell line NSI-1-Ag4-1
- PBS
Phosphate Buffered Saline
- s-PC
Phosphatidylcholine from soy beans
- s-PE
Phosphatidylethanolamine from soy beans
- s-lecithin
lecithin from soy beans 相似文献
18.
Terry L. Riss Kenneth P. Karey B. Daniel Burleigh David Farker David A. Sirbasku 《In vitro cellular & developmental biology. Plant》1988,24(11):1099-1106
Summary A serum-free clonal density growth assay was developed for the quantification of the biological activity of human recombinant
insulin-like growth factor I (IGF-I). The assay measures IGF-I stimulated growth of Balb/c 3T3 cells cultured over 4 d on
poly-d-lysine-coated plastic surfaces in a serum-free medium formulation composed of a 1∶1 (vol/vol) mixture of Ham's F12 and Dulbecco's
modified Eagle's media, supplemented with 3.0 ng/ml bovine basic fibroblast growth factor (bFGF), 10 μg/ml human transferrin,
100 μg/ml ovalbumin, and 1.0 μM dexamethanose. Low-temperature trypsinization of serum-supplemented stock cultures combined with the use of poly-d-lysine-coated plates made it unnecessary to use serum or fibronectin to promote cell attachment and survival. Serum-free
growth conditions were optimized with respect to the concentrations of the supplements. Addition of IGF-I resulted in 3.5-fold
more cells than control cultures without IGF-I after 4 d. Deletion of bFGF resulted in no IGF-I stimulation of growth. The
concentrations of various preparations of IGF-I required to achieve one-half maximal stimulation of cell number (ED50), ranged between 1.25 and 4.7 ng/ml. In parallel assays, IGF-I was 6.6 times more potent than human recombinant insulin-like
growth factor II and 32 times more potent than insulin. When cells were seeded into medium containing IGF-I, transferrin,
ovalbumin, and dexamethasone but no bFGF, growth was minimal. Dose-response addition of bFGF showed an ED50, of 0.9 ng/ml. The methods reported are useful to monitor the biological potency of recombinant and natural-source growth
factors as well as providing a new means of studying the multiple growth factor requirements of Balb/c 3T3 cells in cultures.
This work was supported by a contract from IMCERA Bioproducts, Inc. 相似文献
19.
Microtiter micromass cultures of limb-bud mesenchymal cells 总被引:4,自引:0,他引:4
Douglas F. Paulsen Michael Solursh 《In vitro cellular & developmental biology. Plant》1988,24(2):138-147
Summary A method is described for growing high-density micromass cultures of chick and mouse limb mesenchyme cells in 96-well microtiter
plates (μTμM cultures). Rapid quantitative estimates of chondrogenic expression were obtained by automated spectrophotometric
analysis of Alcian-blue-stained cartilage matrix extracts performed in the wells in which the cells had been grown. Quantitative
estimates of myogenic expression were obtained similarly using anti-sarcomere myosin monoclonal antibody and modified ELISA
techniques. This μTμM-ELISA method may be adapted for use with other antigens for which specific antibodies are available.
These methods were used to compare cartilage and muscle differentiation in 1 to 4 d μTμM cultures grown in serum-containing
(SCM) and defined (DM) media. The DM contains minimal additives (insulin, hydrocortisone, and in some cases, ascorbate or
transferrin) and supports both chondrogenesis and myogenesis. The colorimetric analyses agree well with the morphologic appraisal
of chondrogenesis and myogenesis. Similar numbers of cartilage nodules formed in all cultures, but in DM the nodules failed
to enlarge; explaining the reduced matrix synthesis in DM as compared with SCM, and suggesting that nodule enlargement is
a discrete, serum-dependent step. Studies of selected additives to DM show that transferrin enhances myogenesis, ascorbic
acid enhances chondrogenesis, and retinoic acid inhibits chondrogenesis. Together, the μTμM system, in situ colorimetric assays
of chondrogenesis and myogenesis, and DM will allow rapid prescreening of teratogens and screening of various bioactive compounds
(e.g., hormones, growth factors, vitamins, adhesion factors) for effects on limb mesenchymal cell differentiation.
This work was supported by grants RR08006-13 (DFP) and HD05505 and HD18577 (MS) from the National Institutes of Health, Bethesda,
MD. MF-20 hybridoma supernatant was obtained from the Developmental Studies Hybridoma Bank, Department of Biology, University
of Iowa, Iowa City, Iowa 52242 (maintained by NIH grant NO1-HD62915). 相似文献
20.
John F. Foley Byron Th. Aftonomos 《In vitro cellular & developmental biology. Plant》1988,24(9):900-904
Summary Colonies of HeLa cells cultured in media supplemented with human or bovine serum or both can be morphologically described
as three types: diffuse, intermediate, and compact, with their modal distribution depending on the serum or sera added to
the growth medium. We have observed that for a particular medium or serum system, the percentage of compact colonies remains
fairly constant under normal culture conditions, 0.2%, whereas the diffuse and intermediate colonies vary over a much wider
range. The presence of certain substances as trypsin, heparin and Darvan in the medium favor the increase of compact colonies
at the expense of other types. Furthermore, we have discovered that colonial morphology is influenced by cocultivation of
the HeLa cells with human fibroblastlike cells, the compact colonies increasing as the density of the fibroblast element introduced
into the mixed cultures is increased. Subsequent investigation revealed that conditioned medium from confluent fibroblast
and HeLa cell cultures contained a factor(s), that significantly increased the percentage of compact colonies. The factor
is nondialyzable, heat-stable and can be neutralized by serum. Recorded in this presentation are preliminary observations
on the kinetics of colony formation and the interaction among the three HeLa cell colony types, the diffuse, the intermediate,
and the compact. The factor's effect on HeLa cell colonial morphology is time dependent and rapidly reversed if the factor(s)
is removed and fresh medium added. 相似文献