全文获取类型
收费全文 | 4438篇 |
免费 | 224篇 |
国内免费 | 1篇 |
出版年
2022年 | 14篇 |
2021年 | 27篇 |
2020年 | 14篇 |
2019年 | 20篇 |
2018年 | 36篇 |
2017年 | 37篇 |
2016年 | 64篇 |
2015年 | 96篇 |
2014年 | 125篇 |
2013年 | 488篇 |
2012年 | 222篇 |
2011年 | 235篇 |
2010年 | 161篇 |
2009年 | 151篇 |
2008年 | 227篇 |
2007年 | 264篇 |
2006年 | 238篇 |
2005年 | 264篇 |
2004年 | 304篇 |
2003年 | 242篇 |
2002年 | 249篇 |
2001年 | 45篇 |
2000年 | 45篇 |
1999年 | 57篇 |
1998年 | 51篇 |
1997年 | 53篇 |
1996年 | 35篇 |
1995年 | 46篇 |
1994年 | 54篇 |
1993年 | 58篇 |
1992年 | 52篇 |
1991年 | 40篇 |
1990年 | 29篇 |
1989年 | 35篇 |
1988年 | 39篇 |
1987年 | 34篇 |
1986年 | 42篇 |
1985年 | 45篇 |
1984年 | 43篇 |
1983年 | 39篇 |
1982年 | 47篇 |
1981年 | 51篇 |
1980年 | 40篇 |
1979年 | 23篇 |
1978年 | 26篇 |
1977年 | 22篇 |
1976年 | 30篇 |
1975年 | 15篇 |
1974年 | 19篇 |
1973年 | 19篇 |
排序方式: 共有4663条查询结果,搜索用时 15 毫秒
121.
The effect of implantation of Ehrlich ascites tumor (EAT) cells of creatine distribution was investigated. It was also studied how depletion of creatine by feeding creatine-analogue β-guanidinopropionic acid (β-GPA) affects the growth of EAT cells in mice. Enhanced mobilization of creatine from host tissues to EAT cells against a greater concentration gradient was observed. The creatine (but not creatinine) level in blood plasma was lowered to 22% of the normal value by β-GPA feeding alone and assimilation of 14C-creatine into EAT cells was inhibited. The growth of EAT cells was significantly reduced and the duration of survival of mice after implantation of EAT cells was extended when the creatine concentration was decreased. A decrease in daily food consumption and the degree of muscle atrophy after implantation of EAT cells was less in β-GPA than control groups. In the creatine-depleted mice, the rate of increase in total EAT cell number and the volume of abdominal ascites were approximately half of the control values, and more dead EAT cells were observed. These results suggest that supplementation of β-GPA inhibits creatine transfer to EAT cells and reduces the growth of cancer cells. 相似文献
122.
Inhibition of epidermal growth factor-induced DNA synthesis by tyrosine kinase inhibitors 总被引:10,自引:0,他引:10
Kazuo Umezawa Takashi Hori Hirohisa Tajima Masaya Imoto Kunio Isshiki Tomio Takeuchi 《FEBS letters》1990,260(2):201-205
We prepared methyl 2,5-dihydroxycinnamate as a stable analogue of erbstatin, a tyrosine kinase inhibitor. This analogue was about 4 times more stable than erbstatin in calf serum. It inhibited epidermal growth factor receptor-associated tyrosine kinase in vitro with an IC50 of 0.15 μg/ml. It also inhibited in situ autophosphorylation of epidermal growth factor receptor in A431 cells. Methyl 2,5-dihydroxycinnamate was shown to delay the S-phase induction by epidermal growth factor in quiescent normal rat kidney cells, without affecting the total amount ofDNA synthesis. The effect of erbstatin on S-phase induction was smaller, possibly because of its shorter life time. 相似文献
123.
124.
A plasmid DNA of Anacystis nidulans 6301 was isolated by CsCl-EtBr centrifugation. The Mr of the plasmid, named pBA1, was estimated to be 5.04 +/- 0.26 X 10(6) by electron microscopic analysis and 5.2 X 10(6) by agarose gel electrophoresis. The pBA1 DNA was opened at a unique site with BamHI and cloned in pBR322 vector propagated in Escherichia coli HB101 cells. The recombinant plasmid, named pBAS18, was digested with various restriction endonucleases and its cleavage map was constructed. Based on this result, the cleavage map of the pBA1 plasmid is presented. 相似文献
125.
Kazuo Naka 《Journal of plant research》1982,95(4):385-399
The rates of treefall and canopy opening in the evergreen oak forest in southwestern Japan were determined by studying the
number and size distribution of overstory trees, wind damaged trees, and canopy gaps in a belt transect in the Kasugayama
Forest Reserve in Nara City.
Thirty three percent of the overstory trees wereCastanopsis cuspidata. The total area of canopy gaps was about 20% of the total land area in the study area. The ages of the gaps were determined
by counting the annual rings of various kinds of trees growing in gaps. By comparing gap ages with meteorological data, it
became evident that gap formation was mainly caused by strong typhoons. The mean time interval between strong typhoons visiting
the forest reserve, 6.57 years, was determined by applying the MNY method to the meteorological data.
The treefall rate and the mean area of canopy openings per year were 0.84 overstory trees/ha·year and 55.6 m2/ha·year, respectively. The mean residence time of the forest canopy was about 180 years. 相似文献
126.
Mitsumasa Haruna Makiko Kato Kazuo Ito Toshiaki Nikai Hisayoshi Sugihara Hiroyuki Muratat 《Phytochemistry》1981,20(11):2583-2584
Angeloylcumambrin-B, a new antimicrobial guaianolide sesquiterpene lactone, was isolated from Chrysanthemum ornatum and the structure was determined by a combination of chemical and physical methods. 相似文献
127.
Four known sesquiterpene lactones, tomentosin, ivalin, 4-epi-isoinuviscolide and gaillardin, together with three new lactones, inuchinenolides A, B and C, were identified in the whole plant of Inula britannica var. chinensis. 相似文献
128.
When UDP-[14C]glucose or UDP-[14C]xylose was incubated witha particulate fraction from soybean cells, radioactive polymerswere synthesized. On digestion with Aspergillus oryzae enzymes,these polymers gave 14C-monosaccharides and a 14C-disaccharidewith chromatographic and electrophoretic mobilities indistinguishablefrom those of authentic isoprimeverose (6-O--D-xylopyranosyl-D-glucopyranose).The disaccharide consisted of xylose and glucose, and the latterwas located at the reducing end. Evidence that the disaccharideis isoprimeverose was provided by methylation analysis. Hydrolysisof the methylated disaccharide yielded 2,3,4-tri-O-methyl-D-xyloseand 2,3,4-tri-O-methyl-D-glucose. Thus, incorporation of radioactivityinto isoprimeverose, the smallest structural unit of xyloglucan,suggests that xyloglucan is synthesized in vitro from UDP-glucoseand UDP-xylose. (Received November 20, 1980; Accepted February 14, 1981) 相似文献
129.
Xyloglucan 4-ß-D-glucosyltransferase, an enzyme responsiblefor the formation of the xyloglucan backbone, in a particulatepreparation of soybean cells has been compared with ß-1,4-glucan4-ß-D-glucosyltransferase of the same origin. Thefollowing observations indicate that the enzyme system of xyloglucansynthesis does not contain ß-1,4-glucan 4-ß-D-glucosyltransferaseactivity, although both enzymes transfer the glucosyl residuefrom UDP-glucose to form the ß-1,4-glucosidic linkage:1. The incorporation of [14C]glucose into xyloglucan dependedon the presence of UDP-xylose in the incubation mixture. 2.No measurable amount of radioactivity was incorporated fromUDP-[14C]xylose into the cello-oligosaccharides, although theincorporation of [14C]xylose into xyloglucan depended on thepresence of UDP-glucose in the incubation mixture (Hayashi andMatsuda 1981b). 3. The activity of xyloglucan 4-ß-D-glucosyltransferasewas stimulated more strongly by Mn2+ than by Mg2+, whereas Mg2+was the most active stimulator for the activity of ß-1,4-glucan4-ß-D-glucosyltransferase. 4. An addition of GDP-glucose(100 µM) to the incubation mixture inhibited the activityof xyloglucan 4-ß-D-glucosyltransferase by 17%, whereasthe activity of ß-1,4-glucan 4-ß-D-glucosyltransferasewas inhibited 56% under the same conditions. 5. Irpex exo-cellulasedid not hydrolyze the xyloglucan synthesized in vitro. 6. Theß-1,4-glucan synthesized in vitro was not a branchedxyloglucan because it gave no 2,3-di-O-methyl glucose derivativeon methylation analysis. 7. Pulse-chase experiments indicatedthat the ß-1,4-glucan was not transformed into thexyloglucan. The subcellular distribution of the xyloglucan synthase, however,was similar to that of the ß-1,4-glucan synthase (Golgi-located1,4-ß-D-glucan 4-ß-D-glucosyltransferase).Thus, it appears that the latter enzyme is located at a siteclose to xyloglucan synthase and is set aside for the assemblyof these polysaccharides into the plant cell surface. (Received May 21, 1981; Accepted October 13, 1981) 相似文献
130.
Degradation of Xyloglucan by Wall-bound Enzymes from Soybean Tissue I. Occurrence of Xyloglucan-degrading Enzymes in Soybean Cell Wall 总被引:1,自引:0,他引:1
Koyama Toru; Hayashi Takahisa; Kato Yoji; Matsuda Kazuo 《Plant & cell physiology》1981,22(7):1191-1198
An enzyme preparation that catalyzes the degradation of xyloglucanwas obtained by extraction of the cell walls of soybean hypocotylswith a buffer containing 1.0 M NaCl. The enzyme preparationwas shown to catalyze two-step degradation of xyloglucan. Thepolysaccharide was first degraded into comparatively large fragments,which were then further degraded into monosaccharides. In orderto elucidate the mode of degradation of the xyloglucan duringcell growth, the activities of xyloglucandegrading enzymes ofsoybean-hypocotyl segments were assayed at different stagesof elongation. The total activities of the degrading enzymeswere lower in the elongating regions than in the non-elongatingregions. However, high levels of endo-ß-l,4-glucanasewere found in the elongating regions. These results suggestthat xyloglucan is hydrolyzed by endo-ß-1,4-glucanaseinto comparatively large fragments at the initial stage of growthand the resulting fragments are further degraded into monosaccharidesduring cell elongation. (Received May 20, 1981; Accepted August 8, 1981) 相似文献