全文获取类型
收费全文 | 690868篇 |
免费 | 77391篇 |
国内免费 | 528篇 |
专业分类
768787篇 |
出版年
2016年 | 7575篇 |
2015年 | 11071篇 |
2014年 | 12709篇 |
2013年 | 18067篇 |
2012年 | 20228篇 |
2011年 | 20141篇 |
2010年 | 13580篇 |
2009年 | 12504篇 |
2008年 | 17836篇 |
2007年 | 18655篇 |
2006年 | 17482篇 |
2005年 | 16813篇 |
2004年 | 16433篇 |
2003年 | 15670篇 |
2002年 | 15740篇 |
2001年 | 31854篇 |
2000年 | 32479篇 |
1999年 | 25629篇 |
1998年 | 8687篇 |
1997年 | 9046篇 |
1996年 | 8530篇 |
1995年 | 8154篇 |
1994年 | 7957篇 |
1993年 | 7894篇 |
1992年 | 21213篇 |
1991年 | 20535篇 |
1990年 | 19822篇 |
1989年 | 19186篇 |
1988年 | 18011篇 |
1987年 | 17116篇 |
1986年 | 16039篇 |
1985年 | 16161篇 |
1984年 | 13256篇 |
1983年 | 11386篇 |
1982年 | 8930篇 |
1981年 | 8123篇 |
1980年 | 7436篇 |
1979年 | 12837篇 |
1978年 | 10069篇 |
1977年 | 9159篇 |
1976年 | 8564篇 |
1975年 | 9683篇 |
1974年 | 10502篇 |
1973年 | 10361篇 |
1972年 | 9589篇 |
1971年 | 8448篇 |
1970年 | 7460篇 |
1969年 | 7220篇 |
1968年 | 6553篇 |
1967年 | 5640篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
K. Choi M. D. Burow G. Church G. Burow A. H. Paterson C. E. Simpson J. L. Starr 《Journal of nematology》1999,31(3):283-290
Segregation of resistance to Meloidogyne arenaria in six BC₅F₂ peanut breeding populations was examined in greenhouse tests. Chi-square analysis indicated that segregation of resistance was consistent with resistance being conditioned by a single gene in three breeding populations (TP259-3, TP262-3, and TP271-2), whereas two resistance genes may be present in the breeding populations TP259-2, TP263-2, and TP268-3. Nematode development in clonally propagated lines of resistant individuals of TP262-3 and TP263-2 was compared to that of the susceptible cultivar Florunner. Juvenile nematodes readily penetrated roots of all peanut genotypes, but rate of development was slower (P = 0.05) in the resistant genotypes than in Florunner. Host cell necrosis indicative of a hypersensitive response was not consistently observed in resistant genotypes of either population. Three RFLP loci linked to resistance at distances of 4.2 to 11.0 centiMorgans were identified. Resistant and susceptible alleles for RFLP loci R2430E and R2545E were quite distinct and are useful for identifying individuals homozygous for resistance in segregating populations. 相似文献
992.
993.
D W Hill K J Cureton S C Grisham M A Collins 《European journal of applied physiology and occupational physiology》1987,56(2):206-211
The purpose of this study was to determine the effect of training on the rating of perceived exertion (RPE) at the ventilatory threshold. College students were assigned to either training (n = 17) or control (n = 10) groups. Trainers completed 18 interval training sessions (five X 5 min cycling at 90-100% VO2max) and 8 continuous training sessions (40 min running or cycling) in 6 weeks. Pre- and post-training, cardiorespiratory, metabolic, and perceptual variables were measured at the ventilatory threshold during graded exercise tests on a cycle ergometer. Ventilatory threshold was that point above which VE X VO2-1 increased abruptly relative to work rate. Post-training means of trained and control subjects were compared using analysis of covariance, with pre-training values as covariates. Following training, the adjusted means for the trained subjects were significantly greater (p less than 0.05) than for controls for VO2max (6%), and for work rate (20%), VO2 (23%), and %VO2max (13%) at the ventilatory threshold. However, adjusted means for RPE at the ventilatory threshold were not significantly different (2%). Both before and after training, exercise at the ventilatory threshold was perceived as 'somewhat hard' to 'hard' (RPE = 13-15) by both groups. The relationship between RPE and %VO2max was altered by training, with trained subjects having a lower RPE at a given %VO2max. It is concluded that RPE at the ventilatory threshold is not affected by training, despite that after training the ventilatory threshold occurs at a higher work rate and is associated with higher absolute and relative metabolic and cardiorespiratory demands. 相似文献
994.
995.
Abstract: The enzymatic hydrolysis of UDP-galactose in rat and calf brain was studied. The hydrolysis occurs in two steps: The first is the conversion of UDP-galactose to galactose-1-phosphate catalyzed by nucleotide pyrophosphatase (EC 3.6.1.9), and the second is the conversion of the latter to free galactose by alkaline phosphatase (EC 3.1.3.1). The overall conversion has a pH optimum of 9.0, but there is considerable activity at pH 7.4, which is the optimum for UDP-galactose:ceramide galactosyltransferase in the synthesis of cerebrosides. Preparations from cytosol from calf brain cerebellum or stem that were enriched in UDP-galactose hydrolytic activity inhibit cerebroside synthesis under conditions optimal for the synthesis. Microsome-rich and nuclear debris fractions contain the highest apparent specific activity among the subcellular fractions studied. Hydrolysis of UDP-galactose occurs in all areas of brain, brainstem having the highest activity. The apparent specific activity in jimpy mouse brain homogenate is nearly twice as high as in the control brain homogenate. 相似文献
996.
Colin K.W. Watts Robert L. Sutherland 《Biochemical and biophysical research communications》1984,120(1):109-115
Saturation and competitive binding analyses demonstrated the presence of a high affinity (KD = 0.92 nM), specific antiestrogen binding site (AEBS) in rat liver microsomes and at least 75% of total liver AEBS was recovered in this fraction. When microsomes were further separated into smooth and rough fractions, AEBS was concentrated in the latter. Subsequent dissociation of ribosomes from the rough membranes revealed that AEBS was associated with the membrane and not the ribosomal fraction. Antiestrogen binding activity could not be extracted from membranes with 1 M KCl or 0.5 M acetic acid but could be solubilized with sodium cholate. These data indicate that AEBS is an integral membrane component of the rough microsomal fraction of rat liver. 相似文献
997.
A R Martikian G S Vartanian K G Karagezian 《Biulleten' eksperimental'no? biologii i meditsiny》1984,98(7):33-35
A study was made of the fatty acid composition and the content of triglycerides, phospholipids and nonesterified fatty acids (NFA) in adipose and muscle tissues of rats with alloxan diabetes. The concentration of NFA in alloxan diabetes was found to be considerably reduced in both adipose and muscle tissues. Meanwhile the content of NFA and phospholipids did not experience any substantial changes. The fatty acid composition of triglycerides of the tissues under study was characterized by considerable alterations under diabetes. 相似文献
998.
Effects of atropine on respiratory heat loss in asthma 总被引:4,自引:0,他引:4
Breslin F. J.; McFadden E. R. Jr; Ingram R. H. Jr; Deal E. C. Jr 《Journal of applied physiology》1980,48(4):619-623
999.
A P Weetman M E Holt A K Campbell R Hall A M McGregor 《BMJ (Clinical research ed.)》1984,288(6416):518-520
A study was conducted investigating the possibility that the immunosuppressive action of methimazole (the active metabolite of the antithyroid drug carbimazole) might be due to an effect on the production of oxygen radicals by monocytes. Techniques comprised measurement of luminol dependent chemoluminescence in monocytes and a spectrophotometric assay for production of hydrogen peroxide. The results showed definite inhibition of formation of oxygen radicals by resting and stimulated monocytes, which may explain the immunosuppressive action of the drug in Graves'' disease. The findings also suggest that the formation of oxygen radicals and the initiation of the immune response may be closely related. 相似文献
1000.
The accumulation of gentamicin by rat renal cortex and was not inhibited by probenecid, tetraethylammonium, cephalosporins nor α-aminoisobutyric acid, but was significantly blocked by other aminoglycosides (neomycin, tobramycin and kanamycin). The data suggest that specific binding sites for aminoglycosides are present on the surface or in cells of the renal proximal tubule. 相似文献