全文获取类型
收费全文 | 102090篇 |
免费 | 779篇 |
国内免费 | 891篇 |
专业分类
103760篇 |
出版年
2023年 | 86篇 |
2022年 | 141篇 |
2021年 | 277篇 |
2020年 | 166篇 |
2019年 | 187篇 |
2018年 | 12006篇 |
2017年 | 10798篇 |
2016年 | 7689篇 |
2015年 | 978篇 |
2014年 | 720篇 |
2013年 | 932篇 |
2012年 | 4829篇 |
2011年 | 13347篇 |
2010年 | 12313篇 |
2009年 | 8504篇 |
2008年 | 10168篇 |
2007年 | 11686篇 |
2006年 | 615篇 |
2005年 | 880篇 |
2004年 | 1256篇 |
2003年 | 1272篇 |
2002年 | 1022篇 |
2001年 | 464篇 |
2000年 | 353篇 |
1999年 | 199篇 |
1998年 | 81篇 |
1997年 | 84篇 |
1996年 | 82篇 |
1995年 | 59篇 |
1994年 | 76篇 |
1993年 | 72篇 |
1992年 | 143篇 |
1991年 | 161篇 |
1990年 | 100篇 |
1989年 | 112篇 |
1988年 | 116篇 |
1987年 | 109篇 |
1986年 | 90篇 |
1985年 | 96篇 |
1984年 | 90篇 |
1983年 | 68篇 |
1982年 | 53篇 |
1981年 | 50篇 |
1980年 | 62篇 |
1979年 | 87篇 |
1978年 | 61篇 |
1977年 | 52篇 |
1973年 | 47篇 |
1972年 | 276篇 |
1971年 | 306篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
W Quinkler M Maasberg S Bernotat-Danielowski N Lüthe H S Sharma W Schaper 《European journal of biochemistry》1989,181(1):67-73
Fresh bovine, porcine and canine hearts were homogenized and mitogens for mesoderm-derived cells were purified in three different steps. Extraction by two different ammonium sulfate precipitations was followed by cation-exchange chromatography and by heparin-Sepharose affinity chromatography. A heparin-Sepharose fraction from heart (eluted at 1.1 M NaCl) increased mitotic activity in serum-deprived cultures of porcine aortic endothelial and smooth muscle cells, and in human fibroblasts. This mitogenic activity is potentiated by heparin and inhibited by gamma-interferon. The heart mitogenic fraction showed one double peak on HPLC at A215 and one polypeptide band on SDS/PAGE. These peaks and bands were identical to those obtained from bovine brain. The heart acidic fibroblast growth factor (aFGF) showed a positive signal in Western blots using antibodies raised against brain aFGF. Gas-phase amino acid sequencing established that the mitogens were identical to aFGF and the N-terminally truncated aFGF. Extraction in the presence of a protease inhibitor (pepstatin A) produced a higher-molecular mass form of aFGF with a blocked amino terminus. Another mitogen, eluted at 1.6 M NaCl from heparin-Sepharose, reacted with polyclonal antiserum against human recombinant basic fibroblast growth factor (bFGF) and showed a 66% (12 from 18 amino acids determined by gas-phase sequencing) similarity with bFGF. This polypeptide increased the mitotic activity of the same cell lines but was more potent than aFGF. 相似文献
82.
K D Sharma T M Loehr J Sanders-Loehr M Husain V L Davidson 《The Journal of biological chemistry》1988,263(7):3303-3306
The copper binding site of amicyanin from Paracoccus denitrificans has been examined by resonance Raman spectroscopy. The pattern of vibrational modes is clearly similar to those of the blue copper proteins azurin and plastocyanin. Intense resonance-enhanced peaks are observed at 377, 392, and 430 cm-1 as well as weaker overtones and combination bands in the high frequency region. Most of the peaks below 500 cm-1 shift 0.5-1.5 cm-1 to lower energy when the protein is exposed to D2O. Based on the pattern of conserved amino acids, the axial type EPR spectrum, and the resonance Raman spectrum, it is proposed that the copper binding site in amicyanin contains a Cu(II) ion in a distorted trigonal planar geometry with one cysteine and two histidine ligands and an axial methionine ligand at a considerably longer distance. Furthermore, the presence of multiple intense Raman peaks in the 400 cm-1 region which are sensitive to deuterium substitution leads to the conclusion that the Cu-S stretch is coupled with internal ligand vibrational modes and that the sulfur of the cysteine ligand is likely to be hydrogen-bonded to the polypeptide backbone. 相似文献
83.
The geminate recombination of CO with Hb following dissociation by a 10-ns laser pulse has been studied as a function of pH (9.2 and 7.0 without inositol hexaphosphate and 6.0 with inositol hexaphosphate) and temperature (5-35 degrees C). The hemoglobins studied included adult, Rothschild, rabbit, opossum, and carp. Despite significant differences in their structural and functional properties, the first four of these hemoglobins show similar trends in the yields, rates, and activation energies of the geminate recombination. The nature of the "cage recombination" in hemoglobin is discussed in the light of such findings. Neither a slow diffusion model nor a model based upon a specific non-heme binding site accounts for the observations. 相似文献
84.
A note on some Eurotatoria from Panjab State,India 总被引:1,自引:1,他引:0
Among 35 eurotatorian species presently reported from Panjab State, India, ten species are new records to this region while eight are new records from N. W. India. A new synonym is proposed and biogeographical remarks are made. 相似文献
85.
The flag and second leaves of wheat showed physiological and biochemical differences in the normal and water stressed plants.
Although the flag leaf had lower enzyme activities in the control plants, in stressed plants it could continue nitrate assimilation
better than the second and other leaves. The flag leaf also exhibited a higher tendency to resume normal metabolic activity
after the release of stress as is indicated by higher NRA, NiRa, lower rad and rab. 相似文献
86.
87.
88.
The uptake of nutrients was investigated in the renal cortical brush border membrane (BBM) vesicles at different stages of ascending pyelonephritis. There was significant difference (p less than 0.05) in the uptake of D-glucose, L-alanine, L-aspartate, L-lysine and L-proline 3 days postinfection and onwards in both right unobstructed and left obstructed experimental kidneys as compared to the sham operated control. The uptake of D-glucose, L-lysine and L-proline was found to be significantly decreased (p less than 0.05) during the course of infection. While uptake of L-alanine and L-aspartate increased (p less than 0.05) in early stages and decreased (p less than 0.05) in later stages of infection. The differential effect was attributed to the compensatory measure and different kinds of transport systems for different types of amino acids. 相似文献
89.
The witches' broom disease has been recently observed on poplars in Paris and its suburbs. The incidence of the disease appeared to be considerably high along main roads. The electron microscopic examination of 350 nm thick sieve tube sections revealed the presence of wall-less mycoplasmalike organisms (MLOs) in diseased samples of Populus alba var. nivea Wesm. They could not be found in their healthy counterparts. 相似文献
90.
Underground and aboveground biomass and their ratios at flowering time in different natural stands of Typha angustata near Jaipur, India were studied in the field and experimentally over a period of eleven months (June to April). The underground biomass was 40–50% of the aboveground biomass in both natural and experimental conditions. 相似文献