全文获取类型
收费全文 | 2074篇 |
免费 | 241篇 |
出版年
2021年 | 28篇 |
2020年 | 18篇 |
2019年 | 19篇 |
2018年 | 20篇 |
2017年 | 20篇 |
2016年 | 31篇 |
2015年 | 67篇 |
2014年 | 69篇 |
2013年 | 81篇 |
2012年 | 100篇 |
2011年 | 94篇 |
2010年 | 56篇 |
2009年 | 49篇 |
2008年 | 68篇 |
2007年 | 85篇 |
2006年 | 78篇 |
2005年 | 83篇 |
2004年 | 72篇 |
2003年 | 63篇 |
2002年 | 62篇 |
2001年 | 66篇 |
2000年 | 52篇 |
1999年 | 61篇 |
1998年 | 35篇 |
1997年 | 27篇 |
1996年 | 21篇 |
1995年 | 19篇 |
1994年 | 13篇 |
1993年 | 23篇 |
1992年 | 48篇 |
1991年 | 45篇 |
1990年 | 54篇 |
1989年 | 43篇 |
1988年 | 37篇 |
1987年 | 33篇 |
1986年 | 33篇 |
1985年 | 33篇 |
1984年 | 24篇 |
1983年 | 31篇 |
1982年 | 40篇 |
1981年 | 21篇 |
1980年 | 18篇 |
1979年 | 28篇 |
1978年 | 34篇 |
1977年 | 25篇 |
1976年 | 24篇 |
1975年 | 17篇 |
1974年 | 16篇 |
1973年 | 22篇 |
1968年 | 15篇 |
排序方式: 共有2315条查询结果,搜索用时 15 毫秒
81.
W.F. Harris J.H. Darwin M.J. Newman 《Palaeogeography, Palaeoclimatology, Palaeoecology》1976,19(3):231-248
This paper uses the relative frequencies of occurrence of various types of pollen and spores to indicate the comparative temperatures under which Quaternary sediments accumulated in several locations in New Zealand. The application of association measures, and cluster and discriminant function analysis to such information is described and discussed.The analyses show that the types may be divided into groups whose members vary little with locality or with the statistical methods used to establish them. This stability suggests that anomalous dispersion effects are not a major influence. For some of these groups there is a similarity between the present-day climate of known pollen or spore sources and those of the corresponding groups at the time of deposition. The significant groups are used to summarise the results in pollen diagrams which are compared with similar diagrams for the discriminant function. It is also shown that the methods described assist in locating zone boundaries in a series of samples taken from a bore hole.The results obtained are relevant to the interpretation of samples in which southern beech (Nothofagus fusca type) is the most abundant tree pollen. 相似文献
82.
Marked dental disfigurement and abnormal tooth wear patterns were observed in black-tailed deer (Odocoileus hemionus columbianus) taken from an area near an industrial fluoride source in northwestern Washington. Fluoride levels in the bones of these deer were from 10 to 35 times higher than levels in the bones of normal animals. These levels are similar to those associated with fluorosis of cattle. 相似文献
83.
D J Etherington P B Newman R H Dainty S M Partridge 《Biochimica et biophysica acta》1976,445(3):739-752
Four extracellular proteolytic enzymes (I-IV) (EC 3.4.22.-) were identified in static cultures of Chromobacterium lividum (NCIB 10926) by agar gel electrophoresis and isoelectric focusing. Proteinases I-III were freed of non-enzymic protein by chromatography on TEAE-cellulose and CM-cellulose. The enzyme mixture was then fractionated in a pH gradient by isoelectric focusing. All three enzymes were shown to be heat-labile metallo-enzymes. Optimal activity occurred at pH 5.6 for enzyme I and at pH 6.2 for enzymes II and III. Remazolbrilliant Blue-hide powder was a sensitive substrate for these enzymes. Proteinase I was also shown to degrade haemoglobin and casein effectively, but not myoglobin, ovalbumin or bovine serum albumin. Proteinases I-III exhibited molecular weight values of 75 000, 72 000 and 67 000 by exclusion chromatography and 71 000 and 66 000 by sodium dodecyl sulphate-poly-acrylamide-gel electrophoresis for enzyme I and II, respectively. The amino acid compositions of enzymes I and II were somewhat similar. Proteinase I was inhibited by EDTA, 1,2-di(2-aminoethoxy)ethane-N,N,N',N'-tetraacetic activity. Mg2+ could substitute for Ca2+ or Mn2+ for Co2+. The interrelationship of proteinases I-III is discussed. 相似文献
84.
R J Newman 《BMJ (Clinical research ed.)》1976,2(6033):447-449
Metoprolol and acebutolol, two supposedly cardio-selective beta-adrenergic recptor blocking agents, were tested in healthy volunteers against propranolol, a non-selective drug, for their effect on blood glucose levels during insulin-induced hypoglycaemia. There was not significant difference between propranolol and metoprolol, which both potentiated the initial hypoglycaemic action of the insulin and delayed the return to normoglycaemia. Acebutolol, even though potentiating the initial hypoglycaemia, did not possess a significant delaying effect. A similar trial should be undertaken in diabetics to determine with certainty the safety of such drugs in diabetes mellitus. 相似文献
85.
86.
87.
Contamination transferred into the uterus from external genitalia during artificial insemination (AI) has been hypothesized to cause lowered bovine pregnancy rates (PR). Using aseptic techniques, there is still a possibility of uterine contamination during routine AI. Two experiments were conducted to evaluate the effect of two types of sheath covers (CS) placed over the conventional French Medium Syringe assembly (FMS) used for AI. Their use entailed passing the assembly to the external os of the cervix, pushing the FMS through the CS and manipulating the FMS to the cervical uterine junction in the normal manner. Fifty-six day non-return rate (NRR) in dairy and actual PR in beef cattle were evaluated. In Experiment 1, 30 professional technicians were employed to inseminate 7, 387 dairy cows, while in Experiment 2, six technicians with varying levels of experience inseminated 416 beef cows. Least-squares means for NRR in dairy cattle were 78% using a CS and 79% without. Means for PR in beef cattle were 57% using a CS and 62% without. In Experiment 2, the overall PR was lower in Trial l than in other trials (P<0.05). Since some technicians improved with time, the difference due to trial was attributed to technician variation in gaining experience with a CS. Results indicate that general use of a CS in routine AI of apparently healthy cows will not increase PR. 相似文献
88.
Relation of blood-free to blood-inclusive postmortem lung water measurements in sheep 总被引:2,自引:0,他引:2
Collins J. C.; Newman J. H.; Wickersham N. E.; Vaughn W. K.; Snapper J. R.; Harris T. R.; Brigham K. L. 《Journal of applied physiology》1985,59(2):592-596
Our purpose was to see if the postmortem weight ratio of extravascular lung water to blood-free dry lung (blood-free ratio) was related to similar ratios in blood-inclusive lung and in blood. We developed linear regressions of blood-free ratio on ratios for blood-inclusive lung and blood together and for blood-inclusive lung alone for 73 sheep studied under 11 different protocols and for two subgroups of sheep, one with plasma space expansion and the other without expansion. The relation of ratios of blood-free to blood-inclusive lungs was different between the two subgroups. Although all regressions were highly correlated, the fits of the blood-free ratio on ratios for blood-inclusive lung and blood together were better than for blood-inclusive lung alone. The mean error of prediction of extravascular lung water for all sheep was significantly less for the regression of blood-free ratio on ratios for blood and blood-inclusive lung together (11 g) than for blood-inclusive lung alone (18 g). This study shows that weights of lung homogenate and blood samples before and after simple oven drying can be used to provide accurate inexpensive estimates of postmortem extravascular lung water. 相似文献
89.
90.