全文获取类型
收费全文 | 16024篇 |
免费 | 1807篇 |
国内免费 | 378篇 |
专业分类
18209篇 |
出版年
2023年 | 83篇 |
2022年 | 206篇 |
2021年 | 375篇 |
2020年 | 293篇 |
2019年 | 343篇 |
2018年 | 405篇 |
2017年 | 323篇 |
2016年 | 458篇 |
2015年 | 646篇 |
2014年 | 770篇 |
2013年 | 787篇 |
2012年 | 975篇 |
2011年 | 890篇 |
2010年 | 569篇 |
2009年 | 590篇 |
2008年 | 709篇 |
2007年 | 637篇 |
2006年 | 530篇 |
2005年 | 474篇 |
2004年 | 435篇 |
2003年 | 412篇 |
2002年 | 382篇 |
2001年 | 1209篇 |
2000年 | 1044篇 |
1999年 | 753篇 |
1998年 | 240篇 |
1997年 | 259篇 |
1996年 | 206篇 |
1995年 | 186篇 |
1994年 | 182篇 |
1993年 | 128篇 |
1992年 | 390篇 |
1991年 | 342篇 |
1990年 | 298篇 |
1989年 | 231篇 |
1988年 | 204篇 |
1987年 | 145篇 |
1986年 | 155篇 |
1985年 | 113篇 |
1984年 | 68篇 |
1983年 | 68篇 |
1982年 | 30篇 |
1979年 | 38篇 |
1978年 | 29篇 |
1976年 | 37篇 |
1975年 | 36篇 |
1973年 | 40篇 |
1972年 | 50篇 |
1971年 | 46篇 |
1970年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The use of acetylated cytochrome c in detecting superoxide anion production in rabbit alveolar macrophages 总被引:3,自引:0,他引:3
V N Nasrallah P S Shirley Q Myrvik M Waite 《Journal of immunology (Baltimore, Md. : 1950)》1983,131(5):2104-2106
Polymorphonuclear phagocytes have been shown to undergo marked alteration in oxidative metabolism during phagocytosis. These alterations, collectively known as the "respiratory burst", include increased glucose oxidation through the hexose monophosphate shunt (1), increased oxygen consumption (1), and increased superoxide (O-2)3 (2) and H2O2 production (3). Similar metabolic events have also been shown to occur in the rabbit alveolar macrophage (AM). There is consistent evidence that the macrophage undergoes increased oxygen consumption (4-6) and hexose monophosphate shunt activity (4-9) upon phagocytosis. There are conflicting data, however, concerning the ability of the macrophage to produce O-2. Some studies suggest that macrophages are incapable of producing measurable amounts of O-2 upon phagocytosis (7, 10-12). Other studies, however, suggest that macrophages are indeed capable of producing substantial amounts of O-2 during phagocytosis (8, 13-15). This study was designed to resolve the discrepancies in the literature concerning O-2 production in macrophages. 相似文献
82.
An analysis of the sensitivity of somatic cell hybrids to natural killer cell- and natural cytotoxic cell-mediated lysis 总被引:1,自引:0,他引:1
Y Lin J L Collins P Q Patek M Cohn 《Journal of immunology (Baltimore, Md. : 1950)》1983,131(3):1154-1159
The analysis of the NK and NC sensitivity of somatic cell hybrids formed between parental cell lines that differ in their NK and NC sensitivity has shown the following. 1) The dominant expression of both NK and NC recognition determinants on target cells; 2) the dominant expression of two post-recognitive NC resistance mechanisms, one requiring protein synthesis and one being protein synthesis independent; and 3) the dominant expression of a post-recognitive NK resistance mechanism, which is protein synthesis independent. The post-recognitive protein synthesis-independent NC resistance mechanism confers no NK resistance and the post-recognitive NK resistance mechanism confers no NC resistance. Whether the post-recognitive protein synthesis-dependent NC resistance mechanism confers NK resistance remains open to question. The analysis of the hybrids indicates that transformed cells become sensitive to either NK- or NC-mediated lysis by losing their resistance to the lytic activity of these effector cells, and it appears that differentiation plays a role in determining whether NK or NC resistance will be lost upon transformation. A model is proposed in which the differentiation into a fibroblast associates the loss of NC resistance with transformation, whereas the differentiation into a lymphocyte associates the loss of NK resistance with transformation. Because the loss of NK resistance is not associated with the transformation of fibroblasts, they remain NK resistant, and because the transformation of lymphocytes is not associated with the loss of NC resistance, they remain NC resistant. This provides the basis for the target specificity exhibited by NK and NC effectors. 相似文献
83.
SMAS-platysma face lift 总被引:1,自引:0,他引:1
J Q Owsley 《Plastic and reconstructive surgery》1983,71(4):573-576
Correction of laxity in the submental area and of hypertrophic neck cords has been enhanced with the SMAS-platysma face life over that which was achieved with a standard skin face lift. Evaluation of a 6-year experience with the SMAS-platysma face lift reveals that the operation can be safely performed with an acceptably low incidence of complications. The incidence of hematoma and associated complications is less than that which occurs when cervical and submental defatting is performed in conjunction with a skin face lift. 相似文献
84.
Preparation of [B23-D-alanine]des-(B25-B30)-hexapeptide-insulin by a combination of enzymic and non-enzymic synthesis. 下载免费PDF全文
Des-(B25-B30)-hexapeptide-insulin with B23-glycine replaced by D-alanine was prepared by a combination of enzymic and non-enzymic syntheses. The purified product was homogeneous in polyacrylamide-gel electrophoresis and could be crystallized. The biological activity in vivo of crystalline [B23-D-Ala]des-(B25-B30)-hexapeptide-insulin was determined as 58% of that of standard pig insulin (27 i.u./mg). 相似文献
85.
86.
87.
The presence of Clostridium botulinum in Indonesian waters 总被引:3,自引:0,他引:3
J W Mortojudo E G Siagian F Suhadi B Q Ward W M Ward 《The Journal of applied bacteriology》1973,36(3):437-440
88.
Two fuel utilizers, a strain of Pseudomonas aeruginosa and a Hormodendrum sp., and two fuel isolates which did not use fuel, Staphylococcus and Bacillus spp., were tested for ability to survive and grow in systems containing emulsified or nonemulsified forms of JP-4 jet fuel. Neither emulsion (Alamac no. 1 or Alamac no. 2) supported microbial growth without a water phase. Growth of P. aeruginosa in liquid systems containing either emulsion was not significantly different from growth in liquid systems with nonemulsified fuel. The Hormodendrum sp. grew well in a liquid medium containing nonemulsified JP-4, but when either of the emulsions served as carbon source no growth was observed. However, good growth was noted on spread plates with either emulsion. Viable cells of Bacillus sp. did not increase over a 4-day period, and Staphylococcus sp. did not survive in liquid systems containing JP-4 or emulsions. 相似文献
89.
90.
The susceptibility to Tedion of haploid and diploid-haploid mixtures of eggs of Tetranychus urticae Koch was examined. It was concluded for a normal susceptible strain that haploid eggs are more susceptible to Tedion than diploid eggs. This difference in tolerance between haploid and diploid eggs could not be established for a strain resistant to Tedion.Mass crosses between the susceptible and the resistant strain were made. Susceptible females, mated by resistant males, produce susceptible haploid and resistant diploid offspring. Resistant females, mated by susceptible males, gave a resistant offspring. Both sexes can also transmit resistance to Tedion. As there was a difference in tolerance between diploid offspring in the reciprocal crosses, it is assumed that either a maternal or a cytoplasmic component is also present in the genetical mechanism of Tedion-resistance.
Zusammenfassung Es wurde die Empfindlichkeit haploider und diploid-haploider Gemische von Eiern von Tetranychus urticae Koch gegenüber Tedion untersucht. Für einen normal empfindlichen Stamm wurde aus toxikologischen Daten und einer Verschiebung des Geschlechterverhältnisses erschlossen, daß haploide Eier gegenüber Tedion empfindlicher sind als diploide. Dieser Toleranzunterschied zwischen haploiden und diploiden Nachkommen konnte bei einem gegen Tedion resistenten Stamm nicht nachgewiesen werden.Es wurden Massenkreuzungen zwischen empfindlichen und resistenten Stämmen durch-geführt. Empfindliche Weibchen, mit resistenten Männchen gepaart, produzierten empfindliche haploide und resistente diploide Nachkommen. Resistente Weibchen, mit empfindlichen Männchen gepaart, ergaben eine resistente Nachkommenschaft. Beide Geschlechter können also die Resistenz gegen Tedion übertragen. Da bei den reziproken Kreuzungen ein Toleranzunterschied zwischen den diploiden Nachkommen auftritt, wird angenommen, daß in dem genetischen Mechanismus der Tedion-Resistenz auch eine mütterliche oder eine zytoplasmatische Komponente vorhanden ist.相似文献