全文获取类型
收费全文 | 21655篇 |
免费 | 1715篇 |
国内免费 | 1311篇 |
专业分类
24681篇 |
出版年
2024年 | 59篇 |
2023年 | 471篇 |
2022年 | 631篇 |
2021年 | 591篇 |
2020年 | 661篇 |
2019年 | 812篇 |
2018年 | 837篇 |
2017年 | 688篇 |
2016年 | 666篇 |
2015年 | 717篇 |
2014年 | 1204篇 |
2013年 | 1706篇 |
2012年 | 894篇 |
2011年 | 1189篇 |
2010年 | 1016篇 |
2009年 | 1150篇 |
2008年 | 1124篇 |
2007年 | 1195篇 |
2006年 | 1046篇 |
2005年 | 962篇 |
2004年 | 754篇 |
2003年 | 633篇 |
2002年 | 572篇 |
2001年 | 373篇 |
2000年 | 309篇 |
1999年 | 333篇 |
1998年 | 280篇 |
1997年 | 306篇 |
1996年 | 213篇 |
1995年 | 258篇 |
1994年 | 255篇 |
1993年 | 207篇 |
1992年 | 195篇 |
1991年 | 157篇 |
1990年 | 125篇 |
1989年 | 106篇 |
1988年 | 93篇 |
1987年 | 100篇 |
1986年 | 69篇 |
1985年 | 175篇 |
1984年 | 355篇 |
1983年 | 233篇 |
1982年 | 225篇 |
1981年 | 157篇 |
1980年 | 137篇 |
1979年 | 128篇 |
1978年 | 84篇 |
1977年 | 56篇 |
1976年 | 39篇 |
1974年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Franz-Georg Hanisch Jasna Peter-Katalinic Heinz Egge Ursula Dabrowski Gerhard Uhlenbruck 《Glycoconjugate journal》1990,7(6):525-543
O-Linked glycans were isolated from human skim milk mucins or mucin-derived high-molecular weight glycopeptides and fractionated by anion exchange chromatography into neutral and acidic alditols. Major oligosaccharides contained in the acidic fraction were purified by high performance liquid chromatography and structurally characterized by a combination of fast atom bombardment mass spectrometry, methylation analysis and 500 MHz 1H-nuclear magnetic resonance spectroscopy. The structural aspects exhibited by these major species in the acidic fraction resemble those established previously for the neutral oligosaccharides from human skim milk mucins: 1) the size of the alditols varies from tri- to decasaccharides, 2) the core structure is of the ubiquitous type 2, 3) the backbone sequences are of the poly-N-acetyllactosamine type with a particular preponderance of linearly extended GlcNAc beta(1-3)Gal (major) or GlcNAc beta(1-6)Gal units (minor). 相似文献
82.
Asim Esen 《Journal of Protein Chemistry》1990,9(4):453-460
The immunochemical data from studies with polyclonal antisera to -zein1, the 27 kD component of the maize prolamin, indicated that the region containing 8 tandem repeats of the sequence PPPVHL is an immunodominant site. In one case, the entire antibody repertoire of an antiserum recognized epitope(s) within this region. Three 17-mer oligopeptides corresponding to the predicted antigenic epitopes of -zein1 were synthesized and reacted with three different anti--zein1 sera in order to map antigenic sites in the intact protein. These antisera yielded positive reactions with a 17-mer peptide (peptide 37), which was not in a hydrophilic maximum but derived from the repeat region. The same antisera gave little or no reaction with other peptides (peptides 38 and 39), both of which were in a hydrophilic maximum. In addition, an antiserum to peptide 37 reacted strongly with both the homologous antigen and the intact -zein1. Peptide 37 also blocked the binding of antisera to -zein1 in competition assays. Subsequently, the shorter 6-mer (peptide 82) and 12-mer (peptide 80) versions of peptide 37 were synthesized, and both reacted with anti-peptide 37 serum and also with each of the three anti--zein1 sera. In these reactions and in competition assays, the reactivity and the blocking ability increased in proportion to the length of the peptide. Based on these data, it was concluded that the repeat region of -zein1 is the site of one or more continuous immunodominant epitopes. The data also suggest that the repeat region is exposed on the surface of the folded protein and probably occur as a mobile, random coil. 相似文献
83.
Tatsuo Nakahara Makoto Hirano Takashi Matsumoto Toshihide Kuroki Yoshinori Tatebayashi Tetsuyuki Tsutsumi Kouji Nishiyama Hiroaki Ooboshi Kaoru Nakamura Hiroshi Yao Akio Shiraishi Michinori Waki Hideyuki Uchimura 《Neurochemical research》1990,15(6):609-611
DNA and RNA contents in 20 brain regions or nuclei of the rat were determined by a highly sensitive method using high-performance liquid chromatography with electrochemical detection. The high DNA and RNA contents were found in the hypothalamic nuclei, especially the median eminence-arcuate nucleus. These results may be available for the preparation of nucleic acids as the regional control. 相似文献
84.
A new procedure for non-radioactive detection of single-copy DNA-DNA hybrids combines an existing non-radioactive labeling
and detection kit with a new substrate AMPPD for the enzyme alkaline phosphatase. The main advantages of this procedure are
the possibility to reuse the blots easily and the much shorter detection time compared to radioactive detection methods. 相似文献
85.
Kunio Yonemasu Takako Sasaki Yoshiko Dohi Charles M. Lapière Betty Nusgens 《生物化学与生物物理学报:疾病的分子基础》1990,1096(1):47-51
C1q, a collagen-like complement protein, was purified from the serum of a ddermatosparactic calf which lacks procollagen N-terminal proteinase (pN-proteinase). The specific hemolytic activity of the serum Clq from the dermatosparactic animal was identical to that of C1q from a normal calf. Gel-filtration of serum from dermatosparactic calf, on Sepharose 6B, showed the presence of C1q-antigenic material at only one position which was identical to the elution position of normal bovine C1q. No differdence, under dissociating conditions, could be seen in the size of the chains of C1q in specific immunoprecipitates isolated from the sera of dermatosparactic and normal animals, as judged by polyacrylamidegel electrophoresis (PAGE) in the presence of sodium dodecyl sulfate (SDS). The C1q from the dermatosparactic animal showed the same N-terminal amino acid and typtic-digest peptide pattern on HPLC as C1q from the normal calf. These results strongly suggest that pN-proteinase is not involved in the extracellular processing of C1q. 相似文献
86.
A synchronization treatment was initiated when each of 1227 heifers (four trials) was tailpainted. The tailpaint was sprayed with an aerosol raddle at the end of the treatment period. The heifers were in herds of 20 to 279 animals. Each herd was observed for estrus at selected post treatment intervals. A heifer was considered to be (or to have been) in estrus when the raddle was rubbed off. In three of the trials, animals which had the raddle removed were inseminated at 48h following the end of the synchronization treatment. The tailpaint of an inseminated animal was scored from 0 (less than 10% of the paint remained) to 5 (more than 90% of the paint remained) and was then reraddled with a second color. The detection-insemination sequence was always repeated at 72 and 96h, and sometimes at 120h. Animals which had been previously inseminated, but then had paint scores reduced by at least 2 units were reinseminated 24h later. Over the four trials, 94.5% of the heifers were detected in estrus through the use of the tailpaint and raddle system. The remaining 67 animals included only 10 (0.8%) which had ovulated without being detected in estrus. The reinsemination rate on consecutive days was 11.3% and was highest among animals that had a tailpaint score of 4 or 5 at 48h. The proportion of animals detected in estrus at selected posttreatment intervals varied with the different synchronization treatments used within one herd, or with the same treatment used in different herds. The combination of tailpaint, raddling, tailpaint scoring and reraddling is a simple sequence which can be effectively used to detect estrus among heifers synchronized in research or commercial herds. 相似文献
87.
Anti-bromodeoxyuridine monoclonal antibody: an alternative tool for the identification of replicated DNA at the electron microscope level 总被引:1,自引:0,他引:1
M Thiry D Dombrowicz 《Biology of the cell / under the auspices of the European Cell Biology Organization》1988,62(1):99-102
A new method for identifying the replicated DNA at the electron microscope level is described. Cells were first exposed in vitro to 5-bromodeoxyuridine (BUdR) in conjunction with 5-fluorodeoxyuridine (FUdR) and BUdR incorporated into DNA was then detected on Lowicryl-embedded sections by immunogold technique using a monoclonal anti-BUdR antibody. After using this method, chromatin and chromosomes are strongly labelled. 相似文献
88.
Hubert Felle 《Planta》1988,176(2):248-255
In cells of Zea mays (root hairs, coleoptiles) and Riccia fluitans (rhizoids, thalli) intracellular Ca2+ and pH have been measured with double-barrelled microelectrodes. Free Ca2+ activities of 109–187 nM (Riccia rhizoids), 94–160 nM (Riccia thalli), 145–231 nM (Zea root hairs), 84–143 nM (Zea coleoptiles) were found, and therefore identified as cytoplasmic. In a few cases (Riccia rhizoids), free Ca2+ was in the lower millimolar range (2.3±0.8 mM). A change in external Ca2+ from 0.1 to 10 mM caused an initial and short transient increase in cytoplasmic free Ca2+ which finally levelled off at about 0.2 pCa unit below the control, whereas in the presence of cyanide the Ca2+ activity returned to the control level. It is suggested that this behaviour is indicative of active cellular Ca2+ regulation, and since it is energy-dependent, may involve a Ca2+-ATPase. Acidification of the cytoplasmic pH and alkalinization of the vacuolar pH lead to a simultaneous increase in cytoplasmic free Ca2+, while alkalinization of pHc decreased the Ca2+ activity. Since this is true for such remote organisms as Riccia and Zea, it may be concluded that regulation of cytoplasmic pH and free Ca2+ are interrelated. It is further concluded that double-barrelled microelectrodes are useful tools for investigations of intracellular ion activities in plant cells.Symbols and abbreviations m, m
membrane potential difference, changes thereof
- PVC
polyvinylchloride 相似文献
89.
J. S. Beckmann M. Soller 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1988,76(2):228-236
Summary By making use of pedigree information and information on marker-genotypes of the parent and F-1 individuals crossed to form an F-2 population, it is possible to carry out a linkage analysis between marker loci and loci affecting quantitative traits in a cross between segregating parent populations that are at fixation for alternative alleles at the QTL, but share the same alleles at the marker loci. For two-allele systems, depending on marker allele frequencies in the parent populations, 2–4 times as many F-2 offspring will have to be raised and scored for markers and quantitative traits in order to provide power equivalent to that obtained in a cross between fully inbred lines. Major savings in number of F-2 offspring raised can be achieved by scoring each parent pair for a large number of markers in each chromosomal region and scoring F-1 and F-2 offspring only for those markers for which the parents were homozygous for alternative alleles. For multiple allele systems, particularly when dealing with hypervariable loci, only 10%–20% additional F-2 offspring will have to be raised and scored to provide power equivalent to that obtained in a cross between inbred lines. When a resource population contains novel favorable alleles at quantitative trait loci that are not present (or rare) in a commercial population, analyses of this sort will enable the loci of interest to be identified, mapped and manipulated effectively in breeding programs.Contribution no. 2124-E, 1987 series from The Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel 相似文献
90.
Mycelium ofBeauveria bassiana can be grown in liquid culture, filtered, and the mycelium dried. After rehydration the mycelium sporulates.
Two carbohydrate sources (sucrose and maltose), and one nitrogen/vitamin source (yeast extract) were tested for mycelium growth
and subsequent conidial production. Maximum mycelium growth (12.31 mg/ml), in liquid culture, was in the sucrose (3.5%)/yeast
extract (3.5%) medium, but mycelium from a maltose (2%)/yeast extract (0.75%) medium produced the maximum of 4.62×106 conidia/mg dry mycelium after incubation in moist Petri dishes.
Using the data on mycelium yield (in liquid culture) and conidial production (by dry mycelium) it is calculated that the sucrose
(3.5%)/yeast extract (3.5%) and the maltose (2%)/yeast extract (0.75%) media produce most conidia per media volume (an equivalent
of 3.52–3.72×107 conidia/ml).
相似文献