全文获取类型
收费全文 | 395997篇 |
免费 | 45550篇 |
国内免费 | 360篇 |
专业分类
441907篇 |
出版年
2016年 | 3599篇 |
2015年 | 5399篇 |
2014年 | 6291篇 |
2013年 | 9023篇 |
2012年 | 10004篇 |
2011年 | 10096篇 |
2010年 | 6710篇 |
2009年 | 6342篇 |
2008年 | 8975篇 |
2007年 | 9438篇 |
2006年 | 8985篇 |
2005年 | 8729篇 |
2004年 | 8677篇 |
2003年 | 8270篇 |
2002年 | 8271篇 |
2001年 | 18244篇 |
2000年 | 18798篇 |
1999年 | 14932篇 |
1998年 | 4919篇 |
1997年 | 5171篇 |
1996年 | 4821篇 |
1995年 | 4630篇 |
1994年 | 4560篇 |
1993年 | 4563篇 |
1992年 | 12089篇 |
1991年 | 11662篇 |
1990年 | 11334篇 |
1989年 | 10981篇 |
1988年 | 10364篇 |
1987年 | 9886篇 |
1986年 | 9382篇 |
1985年 | 9475篇 |
1984年 | 7830篇 |
1983年 | 6736篇 |
1982年 | 5360篇 |
1981年 | 4991篇 |
1980年 | 4532篇 |
1979年 | 7642篇 |
1978年 | 6164篇 |
1977年 | 5661篇 |
1976年 | 5343篇 |
1975年 | 6003篇 |
1974年 | 6631篇 |
1973年 | 6577篇 |
1972年 | 6090篇 |
1971年 | 5517篇 |
1970年 | 4763篇 |
1969年 | 4727篇 |
1968年 | 4307篇 |
1967年 | 3629篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
261.
Of 41 fungicides tested in the laboratory, copper carbonate, copper sulphate, mercuric chloride, Agrosan GN, quintozene, kasugamycin, carboxin, pyracar-bolid, carbendazim, chloroneb, benomyl, Ohric, RH 893 (2-n-octyl-4-isothiazole-3-one) and Terrazole were most inhibitory to the mycelial growth of Rhizoctonia solani on Czapek's agar plates and had EC50 values of less than 1 μg a.i./ml, while copper oxychloride, Udonkor, zineb, ziram, F 319 (3-hydroxy-5-methyl isoxazole) and anilazine were much less toxic, ziram being least inhibitory with an EC50 of 214 μg a.i./ml. Of 17 fungicides tested in the greenhouse as seed treatments, thiabendazole, carbendazim, benomyl, thiophanate-methyl, dichlozoline and Ohric gave 80–90% control of damping-off of mung bean seedlings. A single soil drench with thiophanate-methyl and two drenches with benomyl gave about 90% disease control, More seedlings with R. solani infection survived when thiophanate-methyl was used as a post-inoculation soil drench than when benomyl or chloroneb were used. 相似文献
262.
263.
264.
When rats received glucagon or insulin every 2 h after partial hepatectomy (Hx), hepatic putrescine content was increased above control levels at 6 and 12 h, respectively. When the two hormones were combined, the increased levels were additive. Hepatic ornithine decarboxylase activity was above control levels at 12 h after insulin treatment. Hepatic spermidine N1-acetyltransferase activity was enhanced at 6 h only when glucagon was dosed. Putrescine administration from 0 to 4 h or from 6 to 10 h increased hepatic DNA synthesis to similar levels 22 h after Hx. These results suggest that glucagon and insulin additively stimulate hepatic putrescine production after Hx. This may explain the cooperative stimulation of liver regeneration by both hormones. 相似文献
265.
We report a quantification of the maximum mucus accumulation in proliferating rat colonic epithelial cells. The proliferative potential was determined by radioautographic study of one-hour pulse exposures to tritiated thymidine, mucous content was determined by Periodic-acid Schiff (PAS) staining. We examined 55 labeled mucous cells in 0.5- to 1-micrometer serial sections. The maximum thecal and nuclear profiles of these cells were photographed and their surface areas were determined utilizing a coordinate sensor. The data were expressed as a theca-to-nucleus (T/N) ratio. The maximum (T/N) ratio for a labeled mucous cell was 3.0. We performed a similar analysis on 22 unlabeled mucous cells from upper crypt regions and surface epithelium to derive the range of (T/N) ratios for terminally differentiated mature mucous cells. The range of (T/N) ratios from these cells was from 4.8 to 16.4. Our study shows that proliferative potential of mucous cells is determined by the interrelationship between mucus accumulation and nuclear size. 相似文献
266.
Rebecca R. Sharitz Susan A. Wineriter Michael H. Smith Edwin H. Liu 《American journal of botany》1980,67(9):1297-1303
Biochemical phenotsypes of four taxa of Typha from the eastern United States were determined by starch gel electrophoresis. The isozyme banding patterns of T. latifolia, T. angustifolia and T. domingensis are distinct and allow unambiguous species identification when morphological characters are inadequate or unsuitable. The fourth form, T. glauca, is not an F1 hybrid, but it does appear to be intermediate between T. latifolia and T. angustifolia. The status of T. glauca and evolutionary relationships among the four forms may now be clarified by additional sampling because of the distinct and relatively invariant isozyme banding patterns which are described. 相似文献
267.
The presence of the internal parasite (Aphidius matricariae) of the aphid Myzus persicae can be identified by electrophoresis, and staining of several enzyme systems, of which malate dehydrogenase is recommended as the most reliable. It is suggested that the technique could be extended to other small insects, and that pest populations can be screened for percentage parasitism as an adjunct to insecticide and integrated control field trials. 相似文献
268.
269.
270.