全文获取类型
收费全文 | 30264篇 |
免费 | 1297篇 |
国内免费 | 8篇 |
专业分类
林业 | 1069篇 |
农学 | 892篇 |
基础科学 | 174篇 |
4561篇 | |
综合类 | 3977篇 |
农作物 | 1158篇 |
水产渔业 | 1146篇 |
畜牧兽医 | 16478篇 |
园艺 | 335篇 |
植物保护 | 1779篇 |
出版年
2021年 | 222篇 |
2020年 | 265篇 |
2019年 | 331篇 |
2018年 | 600篇 |
2017年 | 664篇 |
2016年 | 566篇 |
2015年 | 364篇 |
2014年 | 552篇 |
2013年 | 1662篇 |
2012年 | 863篇 |
2011年 | 1114篇 |
2010年 | 808篇 |
2009年 | 761篇 |
2008年 | 1077篇 |
2007年 | 1053篇 |
2006年 | 890篇 |
2005年 | 714篇 |
2004年 | 721篇 |
2003年 | 661篇 |
2002年 | 584篇 |
2001年 | 744篇 |
2000年 | 743篇 |
1999年 | 544篇 |
1998年 | 244篇 |
1997年 | 227篇 |
1995年 | 269篇 |
1992年 | 400篇 |
1991年 | 415篇 |
1990年 | 432篇 |
1989年 | 440篇 |
1988年 | 344篇 |
1987年 | 353篇 |
1986年 | 383篇 |
1985年 | 342篇 |
1984年 | 331篇 |
1983年 | 303篇 |
1979年 | 481篇 |
1978年 | 328篇 |
1977年 | 370篇 |
1976年 | 468篇 |
1975年 | 485篇 |
1974年 | 523篇 |
1973年 | 480篇 |
1972年 | 438篇 |
1971年 | 354篇 |
1970年 | 372篇 |
1969年 | 434篇 |
1968年 | 441篇 |
1967年 | 446篇 |
1966年 | 438篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
171.
Surface structures of males and females of Setaria labiatopapillosa were studied by means of scanning electron microscopy at high magnification. It was found that the surface of buccal cavity, lateral appendages, vulva, anus and cloaca differs from the remaining cuticle. The shape of internal and external mouth papillae, amphids, deirids, postdeirid and phasmidial pore was studied. On the surface of the postdeirid are four small papillae arranged in a typical manner around the depression from which projects a needle-like formation. The ventral bands are formed by fine longitudinal parallel folds of the cuticle. Some anomalies in the localization of postcloacal papillae were observed. 相似文献
172.
The independent modes of action of diuron and atrazine on the photochemical activities of chloroplasts (In vivo and in vitro) from the leaves of crop plants Pisum sativum and Pennisetum typhoides and the weeds Amaranthus viridis and Cyperus rotundus were investigated. Hill reaction activity (DCPIP photoreduction) of in vivo chloroplasts (chloroplasts isolated from herbicide-sprayed plants) was unaffected by treatment at sublethal or intermediate levels of diuron or atrazine while that of in vitro chloroplasts (chloroplasts incubated in the required herbicidal concentration) was severely inhibited. The ferricyanide catalyzed noncyclic photophosphorylation was markedly reduced in both the in vivo and in vitro chloroplast systems. N-Methyl phenozonium sulfate (PMS)-mediated cyclic photophosphorylation was inhibited in the in vivo system while a pronounced enhancement of activity was noticed in the in vitro chloroplasts. The rate of NADP+ photoreduction was severely inhibited in the in vitro chloroplasts. The unaffected in the in vivo system. The herbicidal effects on the photoreactions of isolated chloroplasts were compared with chloroplasts isolated from herbicide-sprayed plants. 相似文献
173.
C Graul V Wildenhahn L Lyhs W Lohse 《Archiv fuer experimentelle veterinaermedizin》1976,30(5):643-650
Two experimental groups and series were compared (leghorns and broilers as well as two age groups of broilers) for their adaptive responses to repeated noise application. The noise was 100 dB and applied daily 30 minutes. The reference for comparison was the plasma-11-hydroxycorticosteroid concentration (11-OHKS). The results differed somewhat from those obtained earlier from one first short-time noise application, in that the rise in plasma glucocorticosteroid concentrations dropped from 431 to 210 per cent of the initial values in adult leghorns exposed to repeated noise stress over seven days. Adult broilers, however, did not exhibit any difference in the magnitude of rise of 11-OHKS concentrations by comparison between first and seven days of repeated stress. The initial values, however, were reached earlier by repeated noise application. 相似文献
174.
Bacillary rickettsia-like organisms (BRLO) were found in the tick Dermacentor marginatus. They are gram-negative and differ from common bacteria and reckettsiae both in the cultivation conditions and morphology. BRLO are non-pathogenic for ticks and guinea pigs. In our studies they were isolated on half-engorged females of D. marginatus, on which they are still maintained. 相似文献
175.
Concentrations of dieldrin in aquatic insects, crayfish, minnows, and small carpsuckers, and muscle tissue of channel catfish (Ictalurus punctatus) were compared with the dieldrin content of Des Moines River water in 1971-73. Monthly mean concentrations of dieldrin in river water and most aquatic organisms were highest in June and July, soon after aldrin had been applied to corn land in the watershed. Several groups of aquatic organisms also exhibited high dieldrin levels in the fall when the dieldrin content of river water was seasonally low. The influence of temperature on metabolic rate and enzyme activity and the differences in body fat content were suggested as probable causes of variations observed in the dieldrin content of aquatic organisms. 相似文献
176.
A new syndrome, characterised by acute respiratory distress and by abnormalities of the skin, hair and thyroid, was the apparent cause of neonatal death in 35 (24 per cent) of 146 piglets sired by a large white boar in four small commercial pig units. The syndrome appears to be of genetic origin, inherited as an autosomal recessive trait. Its similarities with the respiratory distress syndrome (RDS) of the newborn infant and the "barker" syndrome of the newborn foal are discussed. 相似文献
177.
A very low virus level was found for a short time in the blood of ducklings and goslings after experimental Lednice (Yaba 1) virus infection by subcutaneous (scut) and intranasal (inas) route and in blood of ducklings also after infection by intracerebral (icer) route. Subsequently virus neutralizing antibody formation was examined. Antibody formation was found in most of animals. In goslings onset of antibody formation seems to be slower than in ducklings after the same virus infection dose; vice versa, in ducklings antibody titer decreased after 6 weeks. Using low infection virus dose, neutralizing antibody level in ducklings was lower than in the former case. On examining the blood and the organs, the virus was detected in a very low amount and for a very short time in blood and spleen of goslings and only in blood of ducklings. 相似文献
178.
L.K. Cutkomp D. Desaiah E.Y. Cheng E.V. Vea R.B. Koch 《Pesticide biochemistry and physiology》1976,6(3):203-208
American cockroaches injected with sublethal doses of DDT (0.75 μg/roach) at 5-day intervals showed a 40% reduction in oligomycin-sensitive Mg2+ATPase from muscle homogenates, and a 23% reduction of Na+-K+ATPase from nerve cords. Thus, the maximum effect measured occurred with the same enzyme and tissue as determined from in vitro studies. The metabolite, DDE, used at 15 μg per roach, gave no significant change in activity of the ATPase system following injection. In contrast, high single doses of DDT (7.5 μg/roach) and 100 μg DDE and dicofol per roach caused over 30% increase in oligomycin-sensitive Mg2+ATPase of muscle and a 10–15% increase in Na+-K+ATPase of nerve cords measured 24 and 48 hr later. While a similar response was observed for Mg2+ATPase activities in cockroaches that were immobilized, the increase in enzyme activities were much greater than that caused by the pesticides. 相似文献
179.
The protective effect of a lyophilized vaccine against Marek's disease ("Keramvac"--Pfizer), prepared from a cell-free turkey's herpesvirus (strain FC 126), was compared in field trials with losses in the group of non-vaccinated chickens. Under the indicated conditions, the vaccine had only a 50.86% effectiveness. The possible causes of the reduced vaccination effect are discussed with regard to the pathomorphological and virological findings suggesting, among others, an increased incidence of the symptoms of the classical form of Marek's disease in the population investigated. 相似文献
180.
V Bergmann 《Archiv fuer experimentelle veterinaermedizin》1975,29(5):717-733
Samples of the two muscles were taken from 8 Landrace fattened pigs, affected with pale, soft exudative meat, during stunning and 15, 30, 45 and 60 minutes after death; also 2, 3, 6, 12, 24 and 48 hours after slaughter, with storage at 20 degrees C for the first six hours and 2-5 degrees C subsequently. Considerable changes were found during the first hour after death, or even in samples taken during stunning, in longissimus dorsi samples. These consisted of destruction of mitochondria and sarcoplasmic reticulum, breakdown of cell membranes, liberation of clumps of fibre protein, disappearance of glycogen, rigor and destruction of capillaries. Such changes would account for the features of pale, soft exudative meat such as water loss, brief rigor, pale colour, deficiency of energy-rich phosphates. By contrast, in the masseter muscles of the same animal these changes did not occur until later, or were in port absent. In both muscle the breakdown of fibres took place by destruction of the "I" bands and the "Z" strips, and this process also commenced in longissimus dorsi before masseter. 相似文献