全文获取类型
收费全文 | 15340篇 |
免费 | 1421篇 |
国内免费 | 968篇 |
专业分类
17729篇 |
出版年
2024年 | 28篇 |
2023年 | 118篇 |
2022年 | 302篇 |
2021年 | 485篇 |
2020年 | 389篇 |
2019年 | 453篇 |
2018年 | 533篇 |
2017年 | 434篇 |
2016年 | 625篇 |
2015年 | 899篇 |
2014年 | 1096篇 |
2013年 | 1132篇 |
2012年 | 1459篇 |
2011年 | 1362篇 |
2010年 | 862篇 |
2009年 | 740篇 |
2008年 | 1012篇 |
2007年 | 934篇 |
2006年 | 836篇 |
2005年 | 714篇 |
2004年 | 678篇 |
2003年 | 559篇 |
2002年 | 478篇 |
2001年 | 290篇 |
2000年 | 232篇 |
1999年 | 176篇 |
1998年 | 130篇 |
1997年 | 100篇 |
1996年 | 70篇 |
1995年 | 60篇 |
1994年 | 58篇 |
1993年 | 26篇 |
1992年 | 58篇 |
1991年 | 44篇 |
1990年 | 42篇 |
1989年 | 36篇 |
1988年 | 44篇 |
1987年 | 24篇 |
1986年 | 24篇 |
1985年 | 20篇 |
1984年 | 18篇 |
1983年 | 20篇 |
1982年 | 15篇 |
1981年 | 20篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1973年 | 6篇 |
1972年 | 8篇 |
1965年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
萌发花生种子子叶肽链内切酶的纯化和性质 总被引:1,自引:0,他引:1
萌发花生种子子叶的肽链内切酶经硫酸铵沉淀,SephadexG-100凝胶层析,DEAE-纤维素23阴离子交换层析和DEAE-SephadexA50层析,得到纯化的酶,该酶有两条同工酶,分子量分别为58和55KD,Km为9.9μmol/L,是半胱氨型肽链内切酶(EC3.4.22),对未萌发花生种子的贮藏蛋白没有明显降解作用. 相似文献
52.
海南坡鹿对生境的选择 总被引:5,自引:0,他引:5
1987~1994年,在海南省大田自然保护区及其外围地带对坡鹿的生境选择性进行了调查,发现坡鹿对自然生境有较强的选择性。对不同的生境的选择频率为:落叶季雨林生境47.93%;灌木草地生境39.14%;有刺灌丛生境10.72%;人工林生境2.21%。还对各种生境进行了评价;并提出了保护生境的对策 相似文献
53.
Cucumber (Cucumis sativus L.) seedlings were grafted onto cucumber-(CG) or figleaf gourd- (FG, Cucurbita ficifolia Bouché)seedlings in order to determine the effect of solution temperature(12, 22, and 32°C) on the mineral composition of xylem sapand the plasma membrane K+-Mg++-ATPase activities of the roots.Low solution temperature (12°C) lowered the concentrationof NO3 and H2PO4 in xylem sap of CG plants butnot of FG plants. Concentrations of K+, Ca++ and Mg++ in xylemsap were less affected than anions by solution temperature.The plasma membrane of FG plants grown in 12°C solutiontemperature showed the highest K+- Mg++-ATPase activity at allATP concentrations up to 3 mM and at low reaction temperatureup to 12°C, indicating resistance of figleaf gourd to lowroot temperature. (Received December 27, 1994; Accepted March 10, 1995) 相似文献
54.
To understand the genetic regulation of vegetative to reproductive transition in higher plants, further characterization of the Arabidopsis mutant embryonic flower1, emf1, was conducted. Using three flowering symptoms, we showed that emf1 mutants could only grow reproductive and not rosette shoots under five different growth conditions. The mutant embryos did not produce the typical tunica–corpus shoot apical structures at the heart-, torpedo-, and mature stages. The divergent shoot apical development during mutant and wild-type embryogenesis indicated that the wild-type EMF1 gene was expressed in early embryogenesis. Mutations in the EMF1 gene affected the embryonic shoot apical development and caused the germinating embryo and regenerating callus to grow inflorescence, instead of rosette, shoots. Our results support the hypothesis that the EMF1 gene regulates the switch between vegetative and reproductive growth in Arabidopsis. 相似文献
55.
Callus cultures and cell suspension cultures derived from Ginkgo biloba L. leaves produced ginkgolidc B. In cell suspension cultures, the production reached a maximum by the 13th day of subculture and followed by a sharp decrease. The medium of Murashige and Skoog induced the highest ginkgolide B content in cultures while the medium of Schenk and Hildebrandt promoted cell growth. For the maximal production of ginkgolide B, cells were cultured in Murashige and Skoog medium modified to contain 1.0 mg/l of -naphthaleneacetic acid, 0.1 mg/1 of kinetin, 30 g/1 sucrose and 1.25 mM potassium phosphate with a molar ratio of ammonium to nitrate ions of 1 3.Abbreviations B5
Gamborg et al (1968) medium
- GKB
Ginkgolide B
- MS
Murashige and Skoog (1962) medium
- NAA
-naphthaleneacetic aicd
- SH
Schenk and Hildebrandt (1972) medium 相似文献
56.
Ergosterol, a membrane sterol found in fungi but not in plants, was used to estimate live mycelial biomass in ectomycorrhizae. Loblolly pine (Pinus taeda L.) seeds were sown in April 1993 and grown with standard nursery culture practices. Correlations between total seedling ergosterol and visual assessment of mycorrhizal colonization were high during July and August but low as ectomycorrhizal development continued into the growing season. Percentages of mycelial dry weight over lateral roots decreased from 9% in July to 2.5% in November because seedling lateral root dry weight accumulated faster than mycelial dry weight. Total ergosterol per seedling increased from July through February. As lateral root dry weight ceased to increase during winter months, ectomycorrhizal mycelia became the major carbohydrate sink of pine seedlings. No distinctive seasonal pattern of soil ergosterol content was observed. The impact of ectomycorrhizal fungi on plant carbohydrate source-sink dynamics can be quantitatively estimated with ergosterol analysis but not with conventional visual determination. 相似文献
57.
58.
59.
N J Oppenheimer M Singh C C Sweeley S J Sung P A Srere 《The Journal of biological chemistry》1979,254(4):1000-1002
The structure of the prosthetic group of citrate lyase (Klebsiella aerogenes) was studied by nuclear magnetic resonance and mass spectrometry. The spectra at 360 MHz of the nucleoside moiety (2'-ribosyladenosine) show the absence of 2'-hydroxyl proton, thus confirming the 2' position as the site of attachment of the second ribose moiety to the dephospho-CoA. This glycosidic linkage is found to be alpha(1" leads to 2') and is identical to that of poly(ADP-ribose). Studies of permethylation products by mass spectrometry support the above conclusion regarding the location of the ribosidic linkage. 相似文献
60.
Synthesis of 4-triazolopyrimidinone nucleotide and its application in synthesis of 5-methylcytosine-containing oligodeoxyribonucleotides. 总被引:7,自引:6,他引:1 下载免费PDF全文
W L Sung 《Nucleic acids research》1981,9(22):6139-6151
5'-0-Dimethoxytritylthymidine (2) was phosphorylated and base-modified simultaneously to yield the 4-triazolopyrimidinone nucleotide (3). Coupling between (3) and other common deoxyribonucleotides gave a fully protected nonamer (4). Deblocking under different conditions yielded the nonamer as phosphodiester with concomitant conversion of 4-triazolopyrimidinone to 5-methylcytosine (aqueous ammonia) or thymine (N1,N1,N3,N3-tetramethyl-guanidinium syn-4-nitrobenzaldoximate solution). 相似文献