首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2741篇
  免费   145篇
  国内免费   2篇
  2021年   21篇
  2020年   9篇
  2019年   16篇
  2018年   26篇
  2017年   21篇
  2016年   49篇
  2015年   87篇
  2014年   87篇
  2013年   196篇
  2012年   145篇
  2011年   160篇
  2010年   90篇
  2009年   97篇
  2008年   133篇
  2007年   158篇
  2006年   139篇
  2005年   173篇
  2004年   178篇
  2003年   165篇
  2002年   162篇
  2001年   39篇
  2000年   37篇
  1999年   54篇
  1998年   38篇
  1997年   43篇
  1996年   31篇
  1995年   37篇
  1994年   32篇
  1993年   25篇
  1992年   28篇
  1991年   23篇
  1990年   28篇
  1989年   27篇
  1988年   38篇
  1987年   18篇
  1986年   20篇
  1985年   23篇
  1984年   15篇
  1983年   23篇
  1982年   30篇
  1981年   20篇
  1980年   23篇
  1979年   18篇
  1978年   13篇
  1977年   8篇
  1976年   17篇
  1975年   14篇
  1974年   13篇
  1973年   9篇
  1967年   5篇
排序方式: 共有2888条查询结果,搜索用时 912 毫秒
111.
112.
A Streptomyces-pepsin inhibitor (S-PI or Pepstatin Ac), and DAN-insensitive carboxyl proteinase was found in a still culture filtrate of Lentinus edodes. The new carboxyl proteinase was purified, and about 9 mg purified enzyme was obtained from 19 liters of culture filtrate, with 11% recovery. The enzyme showed a single band on polyacrylamide gel electrophoresis. The molecular weight and isoelectric point were 40,000 and pH 4.2, respectively. The enzyme did not contain histidine and was composed of 387 amino acid residues. The enzyme was most active between pH 2.7 ~ 2.9, and stable over a pH of 3.2 ~ 5.2 for 3 hr at 37°C. The enzyme was not inhibited by S-PI or synthetic pepsin inhibitors such as DAN and EPNP. The physicochemical and enzymological properties were very similar to those of Scytalidium lignicolum carboxyl proteinase A, which was reported to be an S-PI-, and DAN-insensitive carboxyl proteinase.  相似文献   
113.
114.
From the immature seeds of Phaseolus vulgaris cv. Kentucky Wonder GA1, GA8, GA38, ABA and GA8 glucoside were isolated, and GA4, GA5, GA6 and GA37 were identified by GC or GC-MS. Unknown substance, AB–II, was also suggested to be present in the immature seeds. In the etiolated seedlings glucosyl esters of GA1 and GA38 were identified by GC. GA8 glucoside and AB–II were shown to be present by the histograms.  相似文献   
115.
The absorbability of polyethylene glycol (PEG), a water-soluble nutritional marker, from the gastrointestinal tract of rat was examined using the [14C]-labeled compound ([14C]PEG) having a molecular weight of 4000. Intravenously injected [14C]PEG was readily excreted and recovered almost completely in the urine and neither hepatic nor renal uptake of the PEG was observed. Intragastrically administered [14C]PEG was eliminated in the urine with an average recovery of only 0.43 ± 0.13% (Mean ± S.D., n= 10) of the dose over 24 hr. From the gel column chromatographic profile of the radioactivity excreted in the urine after an oral dose, [14C]PEG was suggested to be absorbed in two forms, as an original form and as a low molecular weight component. The latter component might be the degraded product of PEG in the gastrointestinal tract. From these results it was confirmed that PEG with a molecular weight of 4000 is a satisfactory marker because of its low absorbability.  相似文献   
116.
From the pollen of Zea mays, three brassinosteroids, castasterone, typhasterol and teasterone, were identified by GC/MS and/or 1H NMR. Their concentrations in the pollen were shown by GC/SIM to be about 120 μg/kg fr.wt. (castasterone), 6.6 μg/kg fr.wt. (typhasterol) and 4.1 μg/kg fr.wt. (teasterone). It was also found that the anther contained a fairly large amount of brassinosteroids by a bioassay.  相似文献   
117.
Treatment of N6,N6,5′-O-tribenzoyl-2′,3′-O-isopropylidenetubercidin (VI) with aqueous acetic acid afforded N6,5′-O-dibenzoyltubercidin (V), which was mesylated to yield the dimesylate X. On treatment of X with sodium iodide and zinc dust, the 2′,3′-unsaturated derivatives of tubercidin XI and XIII were obtained.

N6,5′-O-Dibenzoyltubercidin 2′,3′-thionocarbonate (XIV), prepared from V by treatment with Corey-Winter reagent, was converted to the 1-methyl-2′,3′-unsaturated derivative XV in refluxing trimethyl phosphite.  相似文献   
118.
A root growth-promoting factor was isolated from Artemisia capillaris Thunb. The chemical structure of this compound was elucidated as methyl 3-(3-methylbut-2-enoyl)-4-hydroxycinnamate (capillarol) on the basis of its spectroscopic analysis. At 5×10–4m this compound promoted rice root growth to 180% of the control value.  相似文献   
119.
When Rhizopus arrhizus NRRL 1526 was mix-cultured with Proteus vulgaris AHU 1144, a strain having a high fumarase activity, in a medium containing glucose as a substrate, fumaric acid fermentation was successively converted to l-malic acid fermentation and large amounts of l-malic acid were accumulated as an end product.

As an inoculum of P. vulgaris for this fermentation, cells in the stationary growth phase (48 to 72 hr culture) were much more favorable than those in the exponential growth phase (18 hr culture) and malic acid yields in the former case were as high as about 70 to 75 % based on initial glucose after 3 to 4 days of the mixed culture.  相似文献   
120.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号