全文获取类型
收费全文 | 9973篇 |
免费 | 870篇 |
国内免费 | 4篇 |
出版年
2023年 | 41篇 |
2022年 | 72篇 |
2021年 | 171篇 |
2020年 | 97篇 |
2019年 | 132篇 |
2018年 | 161篇 |
2017年 | 158篇 |
2016年 | 266篇 |
2015年 | 436篇 |
2014年 | 501篇 |
2013年 | 562篇 |
2012年 | 802篇 |
2011年 | 778篇 |
2010年 | 499篇 |
2009年 | 455篇 |
2008年 | 638篇 |
2007年 | 548篇 |
2006年 | 531篇 |
2005年 | 428篇 |
2004年 | 458篇 |
2003年 | 431篇 |
2002年 | 413篇 |
2001年 | 112篇 |
2000年 | 130篇 |
1999年 | 102篇 |
1998年 | 106篇 |
1997年 | 83篇 |
1996年 | 83篇 |
1995年 | 69篇 |
1994年 | 54篇 |
1993年 | 72篇 |
1992年 | 76篇 |
1991年 | 77篇 |
1990年 | 60篇 |
1989年 | 58篇 |
1988年 | 52篇 |
1987年 | 60篇 |
1986年 | 58篇 |
1985年 | 68篇 |
1984年 | 54篇 |
1983年 | 59篇 |
1982年 | 42篇 |
1981年 | 46篇 |
1980年 | 50篇 |
1977年 | 47篇 |
1976年 | 40篇 |
1975年 | 40篇 |
1974年 | 42篇 |
1973年 | 42篇 |
1972年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
91.
Analysis of frequencies of single and random multiple transformations in Diplococcus pneumoniae showed that there are at least two transformable units per cell of the total population in highly competent cultures. If 100% of the cells are competent in these cases, the units may be interpreted as the strands of one duplex deoxyribonucleic acid recipient chromosome. The theory is developed to allow for extension to more complex situations. 相似文献
92.
Summary The activity levels of seven enzymes were studied in growing plasmodia of Physarum polycephalum. The enzymes were isocitrate dehydrogenase, glucose-6-phosphate dehydrogenase, glutamate dehydrogenase, acid phosphatase, phosphodiesterase, -glucosidase, and histidase. Six of the enzymes showed a continuous increase in activity during the mitotic cycle; glutamate dehydrogenase exhibited a stepwise increase about 5 h after mitosis. Cycloheximide immediately inhibited the activity of all enzymes. Actinomycin D was ineffective in inhibiting enzyme activity until after one mitotic cycle had been completed; this indicates that mRNA was stable for all of these enzymes during the G2 period. Attempts to induce enzyme activity were unsuccessful.
Zusammenfassung Der Aktivitätsverlauf von sieben Enzymen wurde in wachsenden Plasmodien von Physarum polycephalum untersucht. Es handelte sich um die Enzyme: Isocitrat-Dehydrogenase, Glucose-6-Phosphat-Dehydrogenase, Glutamat-Dehydrogenase, saure Phosphatase, Phosphodiesterase, -Glucosidase und Histidase. Sechs dieser Enzyme wiesen einen kontinuierlichen Aktivitätsanstieg während des Mitosecyclus auf; Glutamat-Dehydrogenase zeigte einen stufenförmigen Anstieg etwa 5 Std nach der Kernteilung. Cycloheximid hemmte sofort die Aktivität der Enzyme, während Actinomycin D erst nach Ablauf eines halben Teilungscyclus inhibierend wirkte. Dies deutet auf eine relativ stabile mRNA hin. Versuche, die Aktivität zu induzieren, schlugen fehl.相似文献
93.
An Improved Diluent for Rubella Hemagglutination and Hemagglutination-Inhibition Tests 总被引:3,自引:2,他引:1
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Angela E. Auletta Gary L. Gitnick Carrie E. Whitmire John L. Sever 《Applied microbiology》1968,16(5):691-694
Rubella hemagglutinating (HA) antigen was prepared in BHK-21 tissue as 5% cell suspensions and from unconcentrated and 20× concentrated infected supernatant fluids. In some instances, unconcentrated fluids were treated with Tween 80 and ether; cell suspensions were treated with ether alone. Preparations were tested for HA activity in dextrose-gelatin-Veronal (DGV) buffer solutions; 0.85% NaCl; Sorenson's phosphate-buffered saline, pH 7.2; and a diluent of 0.9% NaCl, 0.1% CaCl2 (anhydrous), and 0.1% MgSO4·7H2O. HA titers were consistently two- to fourfold higher in the saline with added Ca++ and Mg++ than in DGV. Hemagglutination-inhibition titers of paired human sera were the same in either diluent. It is suggested that the interaction between rubella HA antigen and the red cells of young (less than 1-day-old) chicks may be at least partially ion dependent and that titers are enhanced by increased quantities of divalent cations. 相似文献
94.
95.
INTESTINAL TRIGLYCERIDE ABSORPTION IN THE RAT : An Electron Microscopical Study 总被引:22,自引:16,他引:6
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Robert R. Cardell Jr. Susan Badenhausen Keith R. Porter 《The Journal of cell biology》1967,34(1):123-155
This report provides information on the morphology of fat absorption in rat intestinal epithelial cells. Three types of experiments were performed: (a) intubation of corn oil into fasted rats, (b) injection of physiological fatty-chyme prepared from fat-fed donor rats into ligated segments of jejunum of fasted animals, and (c) administration of electron-opaque particles in corn oil and markers given concurrently with the fat. These results support the hypothesis that fat is absorbed by selective diffusion of monoglycerides and fatty acids from micelles rather than by pinocytosis of unhydrolized triglycerides. Evidence is presented that the pits between the microvilli, previously believed to function in the transport of fat, are not involved in this process. Instead they appear to contribute their contents to lysosomes in the apical cytoplasm. Arguments are offered that the monoglycerides and fatty acids diffuse from the micelle while the latter is associated with the microvillous membrane of the absorptive cell. These micellar components penetrate the plasma membrane and diffuse into the cytoplasmic matrix where they encounter the SER. Triglyceride synthesis occurs in the SER and results in the deposition of fat droplets within its lumina. The synthesis of triglycerides and their sequestration into the SER establishes an inward diffusion gradient of monoglycerides and fatty acids. 相似文献
96.
The interchain disulfide bonds of a human pathological immunoglobulin 总被引:12,自引:0,他引:12
97.
Specializations of the unit membrane 总被引:16,自引:0,他引:16
98.
A study of the chemical structure of the horse immunoglobulins IgG and IgA(T) has shown that the amino acid contents of the peptide chains are very similar. These globulins differ most markedly in the products of papain digestion. IgG gives 3.5s products, whereas IgA(T) gives a 5s fraction and smaller components. This difference appears to be associated with the presence of an additional easily reducible disulphide bond in the Fd fragment of the heavy chain. There is two to three times as much carbohydrate in IgA(T) as in IgG. In both, this is in the heavy chain and in IgA(T) more than half is covalently bound to the Fd fragment. The differences in antigenic specificity between horse IgG and IgA(T) appear to be due to structural differences in the Fc fragment. 相似文献
99.
100.
Studies on the Endoplasmic Reticulum : IV. Its Form and Distribution during Mitosis in Cells of Onion Root Tip 总被引:28,自引:24,他引:4
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Cells of onion and garlic root tips were examined under the electron and phase contrast microscopes after fixation in KMnO4. Special attention was focused on the distribution and behavior of the endoplasmic reticulum (ER) during the several phases of mitosis. Slender profiles, recognized as sections through thin lamellar units of the ER (most prominent in KMnO4-fixed material), are distributed more or less uniformly in the cytoplasm of interphase cells and show occasional continuity with the nuclear envelope. In late prophase the nuclear envelope breaks down and its remnants plus cytoplasmic elements of the ER, which are morphologically identical, surround the spindle in a zone from which mitochondria, etc., are excluded. During metaphase these ER elements persist and concentrate as two separate systems in the polar caps or zones of the spindle. At about this same time they begin to proliferate and to invade the ends of the spindle. The invading lamellar units form drape-like partitions between the anaphase chromosomes. In late anaphase, their advancing margins reach the middle zone of the spindle and begin to fray out. Finally, in telophase, while elements of the ER in the poles of the spindle coalesce around the chromosomes to form the new envelope, the advancing edges of those in the middle zone reticulate at the level of the equator to form a close lattice of tubular elements. Within this, which is identified as the phragmoplast, the earliest signs of the cell plate appear in the form of small vesicles. These subsequently grow and fuse to complete the separation of the two protoplasts. Other morphological units apparently participating in mitosis are described. Speculation is provided on the equal division or not of the nuclear envelope and the contribution the envelope fragments make to the ER of the new cell. 相似文献