全文获取类型
收费全文 | 5955篇 |
免费 | 454篇 |
国内免费 | 2篇 |
专业分类
6411篇 |
出版年
2023年 | 16篇 |
2022年 | 28篇 |
2021年 | 67篇 |
2020年 | 41篇 |
2019年 | 46篇 |
2018年 | 72篇 |
2017年 | 59篇 |
2016年 | 105篇 |
2015年 | 202篇 |
2014年 | 194篇 |
2013年 | 333篇 |
2012年 | 333篇 |
2011年 | 309篇 |
2010年 | 189篇 |
2009年 | 215篇 |
2008年 | 327篇 |
2007年 | 363篇 |
2006年 | 364篇 |
2005年 | 384篇 |
2004年 | 357篇 |
2003年 | 328篇 |
2002年 | 306篇 |
2001年 | 147篇 |
2000年 | 154篇 |
1999年 | 123篇 |
1998年 | 67篇 |
1997年 | 84篇 |
1996年 | 63篇 |
1995年 | 70篇 |
1994年 | 52篇 |
1993年 | 38篇 |
1992年 | 103篇 |
1991年 | 89篇 |
1990年 | 80篇 |
1989年 | 84篇 |
1988年 | 81篇 |
1987年 | 62篇 |
1986年 | 53篇 |
1985年 | 51篇 |
1984年 | 39篇 |
1983年 | 30篇 |
1982年 | 19篇 |
1981年 | 24篇 |
1980年 | 21篇 |
1979年 | 30篇 |
1978年 | 23篇 |
1975年 | 16篇 |
1974年 | 28篇 |
1973年 | 21篇 |
1972年 | 17篇 |
排序方式: 共有6411条查询结果,搜索用时 15 毫秒
101.
Effector phenotype and immunologic specificity of T-cell-mediated adoptive therapy for a murine tumor that lacks intrinsic immunogenicity 总被引:2,自引:0,他引:2
The MCA 102 sarcoma has been defined by a variety of immunologic studies as a tumor lacking intrinsic immunogenicity. Nevertheless, we have recently demonstrated the feasibility of generating therapeutically effective lymphocytes for adoptive immunotherapy of this tumor. Procedures to achieve this required in vivo priming of syngeneic mice to elicit preeffector cells followed by in vitro sensitization (IVS) with tumor cells in the presence of IL-2. By selective depletion of T cell subsets in vivo, we identified the involvement of both CD4+ (L3T4+) and CD8+ (Lyt-2+) T cells in mediating tumor regression. The CD4+ cells exerted their helper function via the secretion of IL-2 because antitumor effects abrogated by depletion of CD4+ cells could be reconstituted by exogenous IL-2. In order to elicit preeffector cells with reactivity against the MCA 102 tumor, we found that in vivo sensitization could be accomplished with either the MCA 102 or MCA 106 tumor but not with the MCA 101 or MCA 105 tumor. Analysis of specificity of tumor stimulation during IVS of MCA 102 tumor-primed preeffector cells demonstrated cross-reactivity between not only the MCA 102 and MCA 106 tumors but also the MCA 105 tumor whereas the MCA 101 tumor was ineffective. In adoptive immunotherapy, transfer of IVS cells generated from MCA 102 tumor-primed and stimulated lymph node cells was able to mediate reductions of pulmonary metastases established from the MCA 102, MCA 105, and MCA 106 tumors but not from the MCA 101 tumor. We conclude that regression of the MCA 102 tumor is probably mediated through T cell recognition of a set of common tumor-associated Ag shared by several other syngeneic tumors. Immunologically, the tumor-associated Ag are characteristically different from classical tumor-specific transplantation Ag (TSTA) because immunity to TSTA on the MCA 105 or MCA 106 tumor does not cross-react with the MCA 102 tumor. Thus, this study demonstrates that Ag other than TSTA on chemically induced tumors can serve as target molecules for T cell-mediated adoptive immunotherapy. 相似文献
102.
Cell-division inhibitor produced by a killer strain of cellular slime mold Polysphondylium pallidum 总被引:1,自引:1,他引:0
The killer strain CK-8 of cellular slime mold Polysphondylium pallidum produces a cell-division inhibitor, in addition to a killer factor. This inhibitor represses cell division of many strains and species of cellular slime molds, except CK-8 itself and its complementary mating-type strain. It is sensitive to both heat and trypsin, and capable of binding to Con A. Its apparent molecular mass is more than 100 kDa. Repression of cell division by this inhibitor is reversed by trypsin treatment of the cells. 相似文献
103.
Tetsuhiro Sakai Toshitaka Ikehara Hiroshi Miyamoto Kenichi Kaniike 《Life sciences》1981,29(23):2429-2436
Growth of HeLa cells cultured with a chemically defined medium was slightly stimulated in the presence of 5% dialyzed calf serum. The growth-promoting action of serum was more conspicuous when cell growth was suppressed in the same medium, in which K+ was replaced by Rb+ to various ratios. The growth-promoting factors(s) of serum was heat-labile. Upon addition of dialyzed serum, passive K+ or Rb+ influx was increased, whereas the active cation uptake was unaffected and cell K+ was rather decreased. The serum did not alter uptake of [3H] amino acids. Also, protein synthesis inhibited in the Rb+-substituted medium was not stimulated significantly, except that observed only when the external K+/Rb+ ratio was . From the distinct effects of serum on cell growth and protein synthesis, we conclude that (i) the serum-induced stimulation of cell growth, which is suppressed in the Rb+-substituted medium, is not a result of the direct effect of serum on synthesis of bulk protein, but a reflection of the effect on another mechanism(s) required for cell growth; and that (ii) this action is basically identical with the growth-promoting action on cells cultured in the normal medium. 相似文献
104.
Cyanide-sensitive and Cyanide-resistant Respiration in the Germination of Cocklebur Seeds 总被引:5,自引:2,他引:3 下载免费PDF全文
Interrelation between the CN-sensitive cytochrome path and the CN-resistant, benzohydroxamic acid (BHM)-sensitive, or n-propylgallate (nPG)-sensitive alternative path in seed respiration during germination was examined using the nondormant upper and lower seeds of Xanthium pensylvanicum Wallr. The operation of both paths was required not only for normal germination of the lower seed but also for KCN- or NaN3-induced germination of both. From the sensitivity to BHM of the germination response, it became obvious that the alternative path exerts its physiological activity as soon as it develops during the early period of water imbibition. Pretreatments with KCN and NaN3 for promoting germination, strikingly decreased only the engagement of the cytochrome path in the subsequent respiration without affecting that of the alternative path. Nevertheless, no germination occurred without the operation of the cytochrome path. This suggested that excess operation of the cytochrome path is detrimental to germination, being maximal following the BHM-sensitive phase. 相似文献
105.
Summary Using bioluminescence of luciferin-luciferase, we showed that ATP leaked out rhythmically from a strand segment ofPhysarum plasmodium made permeable with caffeine-arsenate. With simultaneous measurement of isometric tension rhythm of the strand, it was revealed that the period and phase of oscillation in ATP leakage correspond well with those of tension production. Further, microinjection of luciferin-luciferase into the plasmodial strand indicated that the intracellular luminescence of luciferin-luciferase also oscillates with the same period and in the same phase as the tension rhythm.The free ATP concentration in a homogenate ofPhysarum plasmodium was of the order of 10 M, but if the homogenate was heated in boiling water, the intensity of luminescence suddenly increased 10–100 fold. ATP available for mechanical workin vivo is thus supposed to be at a much lower level than the total average, which was found in the range of 0.2–0.7 mM. 相似文献
106.
Eiji Ichishima Yoshinori Tsuruda Taro Ushijima Takehiko Nomi Shoji Suzuki Michio Takeuchi Akiko Yamane 《Current microbiology》1980,4(2):85-89
The enzymological, physical, and immunological properties of soluble and bound forms of intracellular acid carboxypeptidase
isolated from fresh mycelia ofAspergillus saitoi are reported. In the broken mycelia, about 60% of the total activity was found in the 2,000×g precipitate, with most of the remainder in the 100,000×g supernantant. The highly purified enzymes, Ia and Ib, from the 100,000×g supernatant were found to be homogeneous by such criteria as disc gel electrophoresis at pH 9.4 The bound enzyme, II, was
solubilized from the 2,000×g precipitate by self-digestion at pH 6.4 and was highly purified by chromotography. The two forms of intracellular enzymes,
the soluble enzymes (Ia and Ib) from the 100,00×g supernatant and the solubilized enzyme (II) from the 2,000×g precipitate, were closely related to, but not completely identical with, the extracellular acid carboxypeptidase. 相似文献
107.
An improved culture medium for mouse blastocysts 总被引:7,自引:0,他引:7
Akiko Spindle 《In vitro cellular & developmental biology. Plant》1980,16(8):669-674
Summary Eagle's basal medium, modified to contain essential amino acids at the concentrations optimal for mouse blastocyst hatching,
attachment, and outgrowth, supported in vitro development of the mouse blastocyst better than other tissue culture media tested.
This medium was improved for growth and differentiation of the inner cell mass by doubling the concentration of amino acids
and glucose and by adding uridine (10−5
M) and β-mercaptoethanol (10−5
M). In this improved medium nearly all blastocysts grown from the two-cell stage hatched and formed trophoblast outgrowths,
and 62% developed into two-layer egg cylinders.
This work was supported by the U.S. Department of Energy. 相似文献
108.
109.
The ability of a microsomal enzyme, glucose dehydrogenase (hexose 6-phosphate dehydrogenease) to supply NADPH to the microsomal electron transport system, was investigated. Microsomes could perform oxidative demethylation of aminopyrine using microsomal glucose dehydrogenase in situ as an NADPH generator. This demethylation reaction had apparent Km values of 2.61 X 10(-5) M for NADP+, 4.93 X 10(-5) m for glucose 6-phosphate, and 2.14 X 10(-4) m for 2-deoxyglucose 6-phosphate, a synthetic substrate for glucose dehydrogenase. Phenobarbital treatment enhanced this demethylation activity more markedly than glucose dehydrogenase activity itself. Latent activity of glucose dehydrogenase in intact microsomes could be detected by using inhibitors of microsomal electron transport, i.e. carbon monoxide and p-chloromercuribenzoate (PCMB), and under anaerobic conditions. These observations indicate that in microsomes the NADPH generated by glucose dehydrogenase is immediately oxidized by NADPH-cytochrome c reductase, and that glucose dehydrogenase may be functioning to supply NADPH. 相似文献
110.