全文获取类型
收费全文 | 5749篇 |
免费 | 718篇 |
国内免费 | 452篇 |
专业分类
6919篇 |
出版年
2024年 | 14篇 |
2023年 | 122篇 |
2022年 | 97篇 |
2021年 | 161篇 |
2020年 | 201篇 |
2019年 | 241篇 |
2018年 | 252篇 |
2017年 | 261篇 |
2016年 | 260篇 |
2015年 | 264篇 |
2014年 | 326篇 |
2013年 | 443篇 |
2012年 | 308篇 |
2011年 | 350篇 |
2010年 | 286篇 |
2009年 | 320篇 |
2008年 | 313篇 |
2007年 | 340篇 |
2006年 | 283篇 |
2005年 | 241篇 |
2004年 | 223篇 |
2003年 | 188篇 |
2002年 | 156篇 |
2001年 | 105篇 |
2000年 | 109篇 |
1999年 | 110篇 |
1998年 | 96篇 |
1997年 | 73篇 |
1996年 | 83篇 |
1995年 | 63篇 |
1994年 | 52篇 |
1993年 | 76篇 |
1992年 | 54篇 |
1991年 | 36篇 |
1990年 | 32篇 |
1989年 | 31篇 |
1988年 | 34篇 |
1987年 | 36篇 |
1986年 | 28篇 |
1985年 | 38篇 |
1984年 | 34篇 |
1983年 | 27篇 |
1982年 | 27篇 |
1981年 | 16篇 |
1980年 | 20篇 |
1979年 | 15篇 |
1978年 | 18篇 |
1977年 | 14篇 |
1976年 | 13篇 |
1974年 | 8篇 |
排序方式: 共有6919条查询结果,搜索用时 15 毫秒
81.
Summary A method for quantification of distances between amide hydrogens using only the 3D NOESY-HMQC experiment recorded on a 15N-labelled protein is presented. This method is based on an approximate expression of the NOE intensities between amide hydrogens obtained from continuum modelling of the non-amide spins; this expression is used in a distance calculation algorithm. The algorithm has been named CROWD, standing for Continuum approximation of Relaxati On path Ways between Dilute spins. This approximation as well as the CROWD algorithm are tested on a simulated case; the CROWD algorithm is then applied to experimental data, measured on a fragment of bacteriorhodopsin. 相似文献
82.
Jonathan H. Davis 《Journal of biomolecular NMR》1995,5(4):433-437
Summary 2D 15N-1H correlation spectra are ideal for measuring backbone amide populations to determine amide exchange protection factors in studies of protein folding or other structural features. Most protein NMR spectroscopists use HSQC, which has been shown to be generally superior to HMQC in both resolution and sensitivity. The refocused HSQC experiment is intrinsically less sensitive than the regular HSQC, due to T2 relaxation during the refocusing delays. However, we show here that, when high 15N resolution is needed, an optimized refocused HSQC sequence that utilizes a semi-constant time evolution period and pulsed field gradients has better signal-to-noise ratio and resolution, and integrates more accurately, than a similar HSQC. The differences are demonstrated on a 20 kDa protein. The technique can also be applied to 3D NOESY experiments to eliminate strong NH2 geminal peaks and their truncation artefacts at a modest cost in sensitivity. 相似文献
83.
In fitting of cosine curves latent experimental inequalities due to a serial effect have to be excluded. Though cosinor analysis may be sufficient then, inclusion of biological time, i.e. not fitting values to time but to a function of time, will lead to further improvement. 相似文献
84.
D. W. DUSZYNSKI S. A. ROY J. STEWERT G. A. CASTRO 《The Journal of eukaryotic microbiology》1978,25(3):370-374
SYNOPSIS. Experiments were designed to test whether or not intestinal transit time increases significantly during severe coccidiosis in the rat. Intraduodenal catheters were surgically implanted into 25 rats. Six to 12 days after surgery 11 rats were inoculated orally with 104 sporulated oocysts of Eimeria nieschulzi Dieben, and 11 were inoculated with 106 oocysts; 3 rats were retained as uninfected controls. At 2, 4, 8, 9, and 16 days postinoculation (PI) Na251CrO4 was injected through the catheter into the duodenum of fasted rats and allowed to progress through the small bowel for 15 min, at which time the rats were killed. The distribution of 51Cr in the gut was plotted as a function of gut length. The leading edge of radioactivity traversed 70% of the gut length in controls, and ~ 50–60% in parasitized rats on days 2, 4, 8, and 9 PI. Also, a reflux of gut contents, as evidenced by radioactivity in the stomach, occurred early (PI days 2 & 4) in rats infected with 104 oocysts and throughout patency in rats infected with 106 oocysts. A 2nd study was undertaken to determine if chemically induced suppression of gut transit time during early infection would enhance infectivity as measured by increased parasite fecundity. Nine rats were injected subcutaneously with an antidiarrheal agent, Loperamide®, known to slow small bowel motility significantly. Another group of 9 control rats was injected with the ethanol-propylene glycol solvent. Ten min after injection, all rats were inoculated per os with 104E. nieschulzi oocysts. The daily number of oocysts discharged/rat was followed from PI days 5–11. Patency began for all rats on PI day 7. The total number of oocysts discharged by the drugged rats as compared with controls was not significantly different. 相似文献
85.
A canonical analysis of multiple time series 总被引:2,自引:0,他引:2
86.
The rotational correlation time of two homologous cytoplasmic aspartate aminotransferase molecules isolated from pig and chicken hearts was obtained by spin-labeling technique. The maleimide and iodoacetamide spin-labels modyfying external SH-groups of a protein were used. In the interpretation of ESR spectra a rotational motion of nitroxide group relative to the protein molecule was taken into account. To determine the macromolecule rotational correlation time two methods of the immobilization of a protein molecule were used: 1) by means of increasing protein solution viscosity and 2) by fixation of the protein molecule on adsorbent. From comparison of experimental and theoretical values of rotational correlation time it was conclude that the both enzymes exhibits an intramolecular flexibility. 相似文献
87.
88.
Partial residuals for the proportional hazards regression model 总被引:34,自引:0,他引:34
89.
High performance liquid chromatography (HPLC) was used to follow the kinetics of the alkaline induced opening of the imidazole ring of 7-methylguanosine (7-meGuo). The kinetics show an initial rapid formation of a major transient intermediate and some minor products that were chromato-graphically separable into seven peaks. This phase of the reaction is followed by the formation of a dominant pyrimidine derivative whose liquid chromatography retention time in a 6% methanol, 0.01 M NH4H2PO4 (pH 5.1) solvent is 6 min; during the rest of the reaction time this dominant species was progressively converted to a co-dominant species that has a 4.5-min column retention. Mass spectroscopy confirmed the existence of two species of ring opened 7-methylguanine (7-meGua), one formylated and another deformylated. Schiff's reaction demonstrated that the species in the second HPLC peak is the formylated one. The ring opened 7-methylguanine (rom7Gua) released by formamidopyrimidine (FAPy)-DNA glycosylase was shown to coelute with the formylated species. These results demonstrate that the enzyme excises formylated rom7Gua from DNA Analysis of rom7Guo by NMR showed that there are two signals assignable to methyl protons and two to formyl protons. These chemical shifts were interpreted as being due to the opening of the imidazole ring at two sites and to the formation of formylated and deformylated rom7Gua. 相似文献
90.
高粱泡的生长调控与结实状况 总被引:3,自引:0,他引:3
高粱泡(Rubus lambertionus Ser.)是一种有利用价值的野生果树资源。其优点为:(1)结果早,产量高,亩产量可达500kg以上;(2)适应性广,耐瘠薄,是开发利用低山丘陵的优良资源植物;(3)果实营养丰富,酸味纯正,尤其是所含红色素稳定性好,是加工果汁饮料的优质添加剂;(4)果实采收期在11月中旬到12月底,此时气温低,有利于浆果加工和贮藏,并可利用农闲季节的劳动力。上述特点表明,高粱泡有很好的开发利用前景。但本种在野生状态下蔓生性强,多刺,并具有枝顶生根的习性,因而树形紊乱而松散,栽培时搭架困难,植株占地面积大,而单位面积产量不易提高。为了便于操作管理和提高产量,减少栽培成本,增进经济效益,我们于1990~1991年进行了生长和株形调控试验, 相似文献