全文获取类型
收费全文 | 66935篇 |
免费 | 5380篇 |
国内免费 | 42篇 |
专业分类
72357篇 |
出版年
2023年 | 357篇 |
2022年 | 685篇 |
2021年 | 1253篇 |
2020年 | 952篇 |
2019年 | 1036篇 |
2018年 | 1576篇 |
2017年 | 1351篇 |
2016年 | 2129篇 |
2015年 | 3003篇 |
2014年 | 3011篇 |
2013年 | 3776篇 |
2012年 | 4473篇 |
2011年 | 4094篇 |
2010年 | 2558篇 |
2009年 | 2319篇 |
2008年 | 3031篇 |
2007年 | 2921篇 |
2006年 | 2684篇 |
2005年 | 2904篇 |
2004年 | 2831篇 |
2003年 | 2365篇 |
2002年 | 1982篇 |
2001年 | 1659篇 |
2000年 | 1563篇 |
1999年 | 1383篇 |
1998年 | 664篇 |
1997年 | 593篇 |
1996年 | 654篇 |
1995年 | 529篇 |
1994年 | 510篇 |
1993年 | 478篇 |
1992年 | 1016篇 |
1991年 | 900篇 |
1990年 | 820篇 |
1989年 | 803篇 |
1988年 | 796篇 |
1987年 | 734篇 |
1986年 | 677篇 |
1985年 | 676篇 |
1984年 | 623篇 |
1983年 | 465篇 |
1982年 | 369篇 |
1981年 | 361篇 |
1980年 | 344篇 |
1979年 | 459篇 |
1978年 | 382篇 |
1977年 | 322篇 |
1975年 | 323篇 |
1974年 | 319篇 |
1973年 | 318篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Phage M-1 produced clear plaques with a halo in the lawn of Rhizobium japonicum D211. A one step growth curve of phage M-1 showed a latent period of 3 h, burst size of 55 and rise period of 2 h. The inactivation of phage M-1 was found to be dependent upon the concentraion of d-glucosomanine. The neutralization kinetics of phage M-1 by antiphage serum gave a K value (velocity constant) of 83.1 min–1. Transduction of str and kan was studied in the presence of antiphage serum and d-glucosamine. Cotransduction of different antibiotic resistance markers suggested that the system can be further explored for high resolution mapping in R. japonicum.Abbreviations YM
yeast mannitol medium
- PFU
plaque forming unit
-
moi
multiplicity of infection
- EOP
efficiency of plating 相似文献
992.
993.
Comparison in different species of biliary bilirubin-IX alpha conjugates with the activities of hepatic and renal bilirubin-IX alpha-uridine diphosphate glycosyltransferases. 下载免费PDF全文
The bilrubin-IXalpha conjugates in bile and the activities of bilirubin-IX alpha--UDP-glycosyltransferases in liver and kidney were determined for ten species of mammals and for the chicken. 1. In the mammalian species, bilirubin-IX alpha glucuronide was the predominant bile pigment. Excretion of neutral glycosides was unimportant, except in the cat, the mouse, the rabbit and the dog, where glucose and xylose represented 12--41% of total conjugating groups bound to bilirubin-IX alpha. In chicken bile, glucoside and glucuronide conjugates were of equal importance. They probably represent only a small fraction of the total bile pigment. 2. The transferase activities in liver showed pronounced species variation. This was also apparent with regard to activation by digitonin, pH optimum and relative activities of transferases acting on either UDP-glucuronic acid or neutral UDP-sugars. 3. Man, the dog, the cat and the rat excrete bilirubin-IX alpha largely as diconjugated derivatives. In general, diconjugated bilirubin-IX alpha could also be synthesized in vitro with liver homogenate, bilirubin-IX alpha and UDP-sugar. In contrast, for the other species examined, bilirubin pigments consisted predominantly of monoconjugated bilirubin-IX alpha. Synthesis in vitro with UDP-glucuronic acid, UDP-glucose or UDP-xylose as the sugar donor led exclusively to the formation of monoconjugated bilirubin-IX alpha. 4. The transferase activities in the kidney were restricted to the cortex and were important only for the rat and the dog. No activity at all could be detected for several species, including man. 5. Comparison of the transferase activities in liver with reported values of the maximal rate of excretion in bile suggests a close linkage between conjugation and biliary secretion of bilirubin-IX alpha. 相似文献
994.
995.
996.
Dominique Weil Nguyen Van-Cong Catherine Finaz R. Rebourcet Chantal Cochet J. de Grouchy J. Frézal 《Human genetics》1977,36(2):205-211
Summary 22 independent man-hamster (HGPRT–) hybrids using male human cells with balanced reciprocal translocation t(X;2)(p22;q32) were analysed for human genes localized on chromosome 2 (IDHS, MDHS), on chromosome X (PGK, GAL, G6PD) and for the different chromosomes in relation with the balanced reciprocal translocation (chr.2, chr.2q–, chr.Xp+).The following results were obtained:The chromosomes 2 and 2q– are absent in the 22 hybrids.In 9 hybrids, the absence of MDHS in spite of the presence of the chromosome Xp+ indicates that the gene for MDHS is not localized on this chromosome (or that the gene for MDHS is not on the segment 2q32-2qter translocated on X).In 14 hybrids, the three markers of X (PGK, GAL, G6PD) and IDHS are expressed in the presence of the chromosome Xp+. This result indicates that the genes for these markers are on Xp+ or that the genes PGK, GAL, G6PD are on X without the Xp22-Xter segment, translocated on the chr.2, and that the gene for IDHS is on the 2q32-2qter segment translocated on X.In 8 hybrids, in the absence of the intact chromosome Xp+, the higher percentage of the presence of G6PD (7 hybrids) and the lower percentage of the presence of IDHS (3 hybrids) are explained by the fact that these hybrids selected in HAT medium had to retain a segment of Xp+ bearing the human gene HGPRT. G6PD appeared very close to HGPRT and IDHS very distant from HGPRT.The study of the different correlations between the presence and the absence of these four markers on Xp+ in the different hybrids indicates the following order on the chromosome Xp+ from p to q: IDHs — PGK — GAL — G6PD.
Groupe INSERM: Directeur J. Frézal
Groupe CNRS, ER, 149: Directeur J. de Grouchy 相似文献
Groupe INSERM: Directeur J. Frézal
Groupe CNRS, ER, 149: Directeur J. de Grouchy 相似文献
997.
Arlette Nougarède 《Protoplasma》1977,93(2-3):341-356
Summary In pea axillary meristems submitted to or released from apical dominance, basic nuclear proteins and their fractions (lysine or arginine-rich) were localized at the infrastructural level using convergent methods. In the inhibited nuclei, the condensed chromatin and the nucleoli are the most reactive regions to alcoholic solution of phosphotungstic acid and to ammoniacal silver nitrate. It is the same in the reactivated nuclei after the release from dominance, but the increase in diameter of the nucleoli is accompanied by the creation of a granular component which is observed around the nucleoli during the G1 S or G2 phases. This structure is built up essentially by a lysin-rich ribonucleoprotein complex characteristic of active nuclei. 相似文献
998.
A.J.v.d. Broek A.I.A. Broess M.J.v.d. Heuvel H.P. de Jongh J. Leemhuis K.H. Schonemann J. Smits J. de Visser N.P. van Vliet F.J. Zeelen 《Steroids》1977,30(4):481-510
Using the strategy based on the Hansch method which analyses effects of substituents on biological activity in terms of their hydrophobic, electronic and steric effects we selectively synthesised a series of 11β-substituted-17α-ethynyl-4-estren-17β-ols that combine ease of synthesis with good discrimination between these factors aiming at finding the compounds with optimum biological activity in that series. The compounds were tested quantitatively in the Clauberg test (rabbit) and the ovulation inhibition test (rat). The differences in biological activity could reasonably be correlated with two steric effects introduced by the 11β-substituent. These were a change in the overall shape of the 11β-substituent and the angular methyl group, and direct steric hindrance of the steroid-receptor protein binding. Some exceptions were found possibly due to metabolic conversion of these compounds to the corresponding 11β-substituted-17α-ethynyl-l,5,5(10)-estratriene-5, 17β-diols. 相似文献
999.
Michael Fernandes Gaddo Onesti Roberto Fiorentini Giuseppe Bellini Anne B. Gould Kwan Eun Kim Charles Swartz 《Life sciences》1977,20(4):623-626
Renal hypertension was induced by ligation of the aorta between renal arteries in rats sympathectomized with 6-hydroxydopamine. In the early phase, equally severe hypertension developed in the denervated group as compared to innervated controls. Later, blood pressure was lower in the denervated rats. Initially, increases in plasma renin were seen in both groups; the levels, however, were markedly lower in the denervated rats. Later, the renin levels were similar and not different from baseline. It is concluded that adrenergic neural activity is not essential in the development of renal hypertension; the maintenance of the chronic state, however, depends in part on adrenergic innervation. 相似文献
1000.
Frank A. Smith Dwight E. Gardner Charles L. Yuile Ofelia H. de Lopez Larry L. Hall 《Life sciences》1977,20(7):1131-1138
Rats given 5 ppm F as FAc (equivalent to 26 ppm of NaFac) in the drinking water for approximately four months deposited as much fluoride in the skeletal system as did rats receiving 5 ppm F as NaF in the water. Little evidence could be found for the presence of organically bound fluoride in bone after ingesting FAc, though an appreciable proportion of skeletal fluoride deposited when NaF was ingested was shown not to respond to the fluoride ion electrode. The daily urinary excretion of total fluoride after FAc was somewhat greater than after NaF; about two thirds of this fluoride responded to the electrode, whereas more than 90 percent of the total fluoride after NaF was ionic in nature. The data are interpreted as showing that the rat is capable of splitting the C-F bond in FAc and/or in its fluoride-containing metabolites, with subsequent skeletal storage and renal excretion of the released fluoride ion. The chronic administration of this low level of FAc caused an early but temporary retardation of growth. The Krebs cycle was interfered with, as evidenced by increased concentrations of citrate in the kidney and urine. At termination of the experiment, histological examination of the testes showed that the FAc had induced severe damage characterized by massive disorganization of the tubules, nearly total loss of functional cells, absence of sperm, and damage to the Sertoli cells. 相似文献