全文获取类型
收费全文 | 846656篇 |
免费 | 89944篇 |
国内免费 | 928篇 |
出版年
2018年 | 8030篇 |
2016年 | 12166篇 |
2015年 | 18695篇 |
2014年 | 20729篇 |
2013年 | 26536篇 |
2012年 | 29294篇 |
2011年 | 27816篇 |
2010年 | 19414篇 |
2009年 | 17901篇 |
2008年 | 23907篇 |
2007年 | 24737篇 |
2006年 | 23336篇 |
2005年 | 27479篇 |
2004年 | 26416篇 |
2003年 | 23567篇 |
2002年 | 20963篇 |
2001年 | 32354篇 |
2000年 | 32081篇 |
1999年 | 26331篇 |
1998年 | 9844篇 |
1997年 | 9898篇 |
1996年 | 9308篇 |
1995年 | 8927篇 |
1994年 | 8524篇 |
1993年 | 8607篇 |
1992年 | 22558篇 |
1991年 | 22456篇 |
1990年 | 21998篇 |
1989年 | 21290篇 |
1988年 | 20226篇 |
1987年 | 19177篇 |
1986年 | 18005篇 |
1985年 | 17789篇 |
1984年 | 14709篇 |
1983年 | 12738篇 |
1982年 | 9659篇 |
1981年 | 8698篇 |
1980年 | 8200篇 |
1979年 | 14059篇 |
1978年 | 11233篇 |
1977年 | 10068篇 |
1976年 | 9665篇 |
1975年 | 10848篇 |
1974年 | 12076篇 |
1973年 | 11844篇 |
1972年 | 10821篇 |
1971年 | 10068篇 |
1970年 | 8705篇 |
1969年 | 8605篇 |
1968年 | 8012篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Iu G Kaz'mina S A Salamatova M M Liubinskaia E V Chernokhvostova 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1984,(8):83-88
The possibility of inducing systemic tolerance in animals by feeding them with ovalbumin and human serum was studied on mice, rats and rabbits. Antibodies to ovalbumin, human serum albumin and immunoglobulins (IgG, IgA, IgM) were determined by the passive hemagglutination test in the sera of the test and control animals after the second immunization made through a parenteral route. Tolerance to all the antigens under study was obtained in mice and rats, while in rabbits such feeding was found to produce the priming effect. The degree of tolerance was the greater, the more was the dose of the antigen and the longer was the period of feeding. Different proteins showed varying tolerogenic activity; the same degree of tolerance in mice was obtained by feeding them with IgG in a dose of 0.3-0.5 mg and with ovalbumin or human serum albumin in a dose of 6-12 mg (per gram of body weight). Tolerance was determined on day 3 after the course of feeding was over; in 3 weeks tolerance essentially decreased, and in 1.5-2 months it was replaced by normal reactiveness. Tolerance induced by the oral administration of antigens proved to be immunologically specific. 相似文献
992.
The population dynamics of Heterodera glycines as influenced by alachlor, fenamiphos, and ethoprop alone and in herbicide-nematicide combinations were studied in the field. Numbers of H. glycines juveniles and eggs were higher at midseason and harvest where nematicides were applied. Fenamiphos alone or in combination with alachlor provided better control of H. glycines and greater seed yields than treatments with ethoprop. Numbers of H. glycines eggs at harvest in 1980 were positively correlated with numbers of juveniles at planting in 1981 and negatively related to seed yield in 1981. 相似文献
993.
The isolation and identification of a material present in the plasma of hypertensive dogs and hypertensive human patients has been under study since 1972. The earliest experiments in relation to this work, noted that plasma from hypertensive dogs cause a hyperresponse to norepinephrine when both were administered by way of the vein. Employing a rat assay system that consisted of an anesthetized rat with polyethylene catheters in the vein for giving norepinephrine and the test fractions and a catheter in the artery for blood pressure monitoring, fractions from hog kidney were tested for hyperresponsiveness activity. The active material is very comparable to cyclic AMP in molecular weight, ultraviolet spectrum, paper chromatography, Enzyme hydrolysis and activity in the anesthetized rat system. This evidence indicates that the hyperresponsiveness factor of renal origin is cyclic AMP. 相似文献
994.
G E Tranter 《Bio Systems》1987,20(1):37-48
The violation of parity by the weak interactions ensures that enantiomeric chiral molecules have inequivalent energies, one being inherently stabilized with respect to the other. These parity-violating energy differences have been calculated for a number of fundamental biomolecules including a series of alpha-amino acids, polypeptide structures, and a representative of the sugar series together with its variation over a possible prebiotic reaction path leading to alpha-amino acids. In each case the natural enantiomer found in terrestrial biochemistry was shown to be intrinsically stabilized and preferred over its unnatural enantiomer. The significance of these results in accounting for the prebiotic origins of the terrestrial biomolecular homochirality is discussed and the possible consequences of parity-violating energy differences in mineral catalysts during the prebiotic era considered. 相似文献
995.
Cell division in fertilized sea urchin eggs was reversibly inhibited when the ketoaldehyde phenyl glyoxal (PG) at a concentration of 0.1 mM was added to eggs for ten minutes prior to the formation of the mitotic spindle. We investigated whether inhibition of mitosis was due to PG binding to the cell surface (as previously suggested by Stein and Berestecky, '74) or to some intracellular effect. When 14C-PG was added to eggs, label was readily taken up into the egg cytoplasm; very little label was associated with the egg surface. In the cytoplasm PG combined with equimolar amounts of reduced glutathione (GSH), decreasing the levels of cellular GSH to less than 15% of normal and accounting for at least 50% of the PG taken up by eggs. The concentrations of oxidized and protein-bound glutathione were unaffected by PG treatment. We showed that glyoxalase enzymes were present in sea urchin eggs and were capable of metabolizing the PG-GSH complex, thereby restoring GSH to normal levels after PG was removed from the sea water. Though some other effect of PG cannot be ruled out, the major fate of PG in eggs was to combine with GSH, and the transient decrease in GSH which resulted could lead to inhibition of mitosis. While other reports (Nath and Rebhun, '76; Oliver et al., '76) have shown that reagents which oxidize GSH disrupt microtubule-related events, our results showed that such inhibition could be caused by decreased GSH levels alone. 相似文献
996.
R Page L W Frazier T Yorio 《Comparative biochemistry and physiology. A, Comparative physiology》1988,91(1):53-59
1. The northern leopard frog, Rana pipiens, pipiens, in contrast to the southern leopard frog, Rana pipiens, berlandieri, did not demonstrate any significant H+ excretion across its integument even during a challenge of chronic metabolic acidosis. Likewise, no increase in the number of H+ secreting mitochondria-rich cells were observed in the northern frogs. 2. Under normal acid-base conditions in the southern frogs, H+ excretion was found to be dependent on mucosal sodium concentrations, whereas during chronic metabolic acidosis, H+ excretion was independent of mucosal sodium concentrations, but was amiloride sensitive. 3. High salinity adapted southern frogs, under normal and acidotic conditions, had enhanced H+ excretion rates as compared to the control non-salt adapted frogs. 4. Blood analyses demonstrated that significant acid-base changes were the result of systemic acidosis and not due to salt adaptations. Blood Na+ and K+ concentrations were also efficiently maintained during salt adaptations or chronic metabolic acidosis. 5. The results suggest that H+ excretion in epithelia can be influenced by the sodium transport state of the cell and the systemic acid-base profile. Models are proposed explaining these relationships. 相似文献
997.
ROBIN M. OVERSTREET WILLIAM E. HAWKINS JOHN W. FOURNIE 《The Journal of eukaryotic microbiology》1984,31(2):332-339
Calyptospora n. g. was erected for Eimeria funduli because the sporocyst of that species lacks Stieda and sub-Stieda bodies, has a veil supported by sporopodia, and has an anterior apical opening. A suture may be present, but it does not completely divide the sporocyst into two valves. Because C. funduli has an obligatory invertebrate intermediate host, we established Calyptosporidae n. fam. to accommodate Calyptospora and tentatively to accept Goussia. A new subgenus, Plagula, is erected for species of Goussia with a sporocystic veil not supported by sporopodia. We consider the family more primitive than Eimeriidae, Sarcocystidae, and possibly Lankesterellidae. 相似文献
998.
999.
The finger and palmar prints of 60 women with breast carcinoma were studied. The results were compared with two groups of
healthy women, the first consisted of old women and the second of young women. The dermatoglyphics seem to be of little use
in the diagnosis of cancers of ectodermic origin.
Supported by M.P.I. 60%, 1983 相似文献
1000.
L Cohen-Solal J Castanet F J Meunier M J Glimcher 《Comparative biochemistry and physiology. B, Comparative biochemistry》1986,83(2):483-486
Extent of prolyl hydroxylation in newly synthesized viper collagen is decreased at 10 degrees C to approximately 23% of normal on skin and to approximately 57% of normal in bone collagen. At 20 degrees C, prolyl hydroxylation is approximately 50% of normal in skin and normal in bone. At 10 degrees C and 20 degrees C, prolyl hydroxylation is decreased approximately 32% in the skin collagen of carp. In contrast, prolyl hydroxylation is unchanged at 10 and 20 degrees C in bone, scale and lepidotrichia. Prolyl hydroxylation of cartilaginous endoskeleton showed an approximately 25% decrease at 20 degrees C. 相似文献