全文获取类型
收费全文 | 7620篇 |
免费 | 582篇 |
国内免费 | 7篇 |
出版年
2022年 | 41篇 |
2021年 | 110篇 |
2020年 | 66篇 |
2019年 | 80篇 |
2018年 | 106篇 |
2017年 | 106篇 |
2016年 | 194篇 |
2015年 | 299篇 |
2014年 | 347篇 |
2013年 | 494篇 |
2012年 | 485篇 |
2011年 | 489篇 |
2010年 | 310篇 |
2009年 | 336篇 |
2008年 | 451篇 |
2007年 | 448篇 |
2006年 | 441篇 |
2005年 | 412篇 |
2004年 | 439篇 |
2003年 | 421篇 |
2002年 | 363篇 |
2001年 | 165篇 |
2000年 | 141篇 |
1999年 | 147篇 |
1998年 | 83篇 |
1997年 | 59篇 |
1996年 | 54篇 |
1995年 | 50篇 |
1994年 | 62篇 |
1993年 | 65篇 |
1992年 | 103篇 |
1991年 | 79篇 |
1990年 | 70篇 |
1989年 | 62篇 |
1988年 | 52篇 |
1987年 | 55篇 |
1986年 | 48篇 |
1985年 | 55篇 |
1984年 | 53篇 |
1983年 | 35篇 |
1982年 | 29篇 |
1981年 | 35篇 |
1980年 | 29篇 |
1979年 | 26篇 |
1978年 | 23篇 |
1977年 | 21篇 |
1976年 | 18篇 |
1975年 | 16篇 |
1973年 | 16篇 |
1972年 | 16篇 |
排序方式: 共有8209条查询结果,搜索用时 46 毫秒
141.
I Patty F Tárnok L Simon T Jávor G Deák S Benedek P Kenéz L Nagy G Mózsik 《Acta physiologica Hungarica》1984,64(3-4):379-384
The gastric cytoprotective effects of vitamin A, De-Nol and sucralfate were compared with the effectiveness of pirenzepine in healing ulcer in patients with chronic gastric ulcer. A total of 100 patients was randomized into different groups: the patients were treated with antacids, vitamin A (3 X 50.000 IU), De-Nol liquid (4 X 5 ml), sucralfate (4 X 1 g) or pirenzepine (3 X 50 mg). The treatment was continued for 4 weeks. At the beginning, 2 and 4 weeks after starting treatment the patients were subjected to endoscopy and the size of the ulcer was measured planimetrically. The ulcer-healing effect of De-Nol liquid was significantly better than that of the antacids (p less than 0.01). Ulcer size was reduced significantly in all groups (p less than 0.01), however, at the end of the study the gastric ulcers were smallest in the De-Nol treated group (p less than 0.001). The dynamics of ulcer healing in the second week was most favourable in the patients receiving vitamin A (p less than 0.01). The present data point to the cytoprotective effects of De-Nol liquid, vitamin A and sucralfate and to their ability of healing chronic gastric ulcers. 相似文献
142.
Purification and characterization of two forms of microsomal carbonyl reductase in guinea pig liver. 总被引:1,自引:0,他引:1
Glycosaminoglycan oligosaccharides generated by treatment of biosynthetically radiolabelled dermatan sulphate and hyaluronic acid with chondroitin AC lyase or testicular hyaluronidase may be resolved into a series of discrete bands by polyacrylamide-gel electrophoresis. Bands were identified by fixation in glacial acetic acid containing 20% (w/v) 2,5-diphenyloxazole followed by fluorography. The bands represented glycans which differed in size by one disaccharide unit. For the larger oligosaccharides (decasaccharides and above) of similar charge: mass ratio, there was a linear relationship between electrophoretic mobility and log Mr. However, the smaller species showed anomalous migration patterns. Consideration of the structures of the fragments produced by the different enzyme treatments suggests that copolymeric and homopolymeric oligosaccharides may be separated by polyacrylamide-gel electrophoresis. There are many potential applications of this technique, foremost amongst them being studies on the molecular size heterogeneity and patterns of enzyme-mediated depolymerization of native glycosaminoglycan chains and investigations into rates of polymer chain elongation and post-polymerization modification reactions so essential to glycosaminoglycan function. 相似文献
143.
Purification of bacterial L-methionine gamma-lyase 总被引:1,自引:0,他引:1
A chromatographic procedure using sequential ion-exchange columns is described for separating choline, trimethylamine, trimethylamine oxide, and betaine extracted from marine fish tissues; added exogenous carnitine can also be separated by the system. Choline with its positive charge binds to the AG 50W-X8 (Na+, pH 9) column. The column is first eluted with 0.1 N NaOH to collect trimethylamine, trimethylamine oxide, and betaine; choline is then eluted with 0.5 N NaOH. The amines collected with 0.1 N NaOH are subsequently separated using an AG 50W-X8 (H+, pH 4) column eluted with a linear 0-1 M NaC1 gradient. 相似文献
144.
Spheroplasts ofHalobacterium cutirubrum were formed upon suspension of cell pellets in 0.1M MES buffer, pH 7.0, containing 0.5M sucrose, 0.25M NaCl, and 0.01M MgCl2. The spheroplasts regenerated into rod-shaped bacteria when plated on a complex medium containing 15% (wt/vol) sucrose, undergoing several divisions as spherical bodies before the rod shape developed. The frequency of regeneration was approximately 5% of the total spheroplasts plated. The yield of regenerants was increased significantly (to approximately 35%) when bovine serum albumin was present in the spheroplasting buffer and dilution media. The conditions for spheroplast formation and regeneration inH. cutirubrum were also found effective forHalobacterium salinarium but not forHalobacterium halobium.NRCC Paper no. 23080. 相似文献
145.
The carbon magnetic resonance spectra of many fatty acid methyl esters with cis and trans double bonds and triple bonds at various positions and in many different combinations have been investigated.The influence of the ester group on double and triple bonds in the fatty acid chain depends strongly on the positions of these bonds. For a given position the influence is constant, even if one or more other double or triple bonds are present.Together with the evaluated chemical shift parameters for the effects of double and triple bonds on each other, complete assignments are possible and spectra of various types of unsaturated esters can be predicted with high accuracy (±0.1 ppm). 相似文献
146.
A procedure to remove protease activities from Bacillus subtilis sporulating cells and their crude extracts. 总被引:6,自引:0,他引:6
A simple procedure was developed to remove both extracellular and intracellular proteases associated with aporulating Bacillus subtilis cells. Cells are washed four times with 1 m KCl before breakage and their crude extracts are treated with 2 mm diisopropylfluorophosphate before passage through a hemoglobin-Sepharose affinity column. RNA polymerase in crude B. subtilis extracts treated by this procedure was stable, functionally and structurally, for more than 1 month at 4°C. This process for removing all proteases should work essentially with any crude extracts containing proteolytic activities. 相似文献
147.
Male, albino, Sprague-Dawley rats were sacrificed by cervical separation. Segments of jejunum were excised, everted and examined with the electron microscope. Examination of tissue fixed immediately after eversion revealed the following changes as compared to non-everted segments fixed and : 1) an increase in the length of microvilli from (mean ± S. E.) 0.991 ± 0.011μ for normal tissue to 1.389 ± 0.023μ for everted tissue, 2) an increase in width of microvilli from (mean ± S. E.) 0.089 ± 0.001μ for normal tissue to 0.097 ± 0.001μ for everted tissue, 3) an increase in length and number of lateral membrane interdigitations, and 4) the appearance of intercellular “lakes” in the lateral spaces. The above changes are in those structures hypothesized to be involved with salt and water transport across epithelia and may reflect altered transport rates as compared to . 相似文献
148.
Summary Several classes of mutants derived from facultative methylotrophs, Microcyclus eburneus and Protaminobacter ruber, accumulate 0.5–3.8 mg/ml of O-methyl-L-homoserine (OMH) in a medium containing methanol as sole carbon source. The wild-type parent strains also accumulate OMH when the medium is supplemented with L-homoserine; the accumulation of OMH by the mutants is ascribed to an increased L-homoserine pool. 相似文献
149.
Hiromichi Kayano Isao Karube Tadashi Matsunaga Shuichi Suzuki Ooki Nakayama 《Applied microbiology and biotechnology》1981,12(1):1-5
Summary A blue-green algae, Anabaena N-7363, was immobilized in 2% agar gel. The hydrogen productivity of the immobilized algae was three times higher than that of free algae. The maximum hydrogen production rate by the immobilized blue-green algae was 0.52 moles h–1 g–1 (of wet gel) in the medium without nitrogen sources under illumination (10,000 lux). The oxygen evolved was then removed by a reactor containing aerobic bacteria. A photo-current of 15–20 mA was continuously produced for 7 days by the photochemical fuel cell system consisting of the immobilized Anabaena reactor, the oxygen-removing reactor and the hydrogen-oxygen fuel cell. The conversion ratio of hydrogen to current was from 80% to 100%. 相似文献
150.
Masakiyo Iwai Hiroshi Kanno Masashi Hashino Jinichi Suzuki Takumi Yanaihara Tetsuya Nakayama 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1981,225(2)
A simple, rapid and highly specific method by selected ion monitoring (SIM), using 9α,11α-[2H2]estrone, [2,4-2H2]estradiol-17β and 2,4-[2H2]estriol as internal standards, was developed for the determination of serum estrogens during pregnancy. Serum samples were submitted to a simple extraction procedure and were analysed after formation of the trifluoroacetic anhydride derivative. The inter-assay coefficients of variation for estrone, estradiol-17β and estriol were 3.73%, 3.42% and 3.49%, respectively. The results obtained by SIM were compared with analysis performed using radioimmunoassay. 相似文献