全文获取类型
收费全文 | 7362篇 |
免费 | 1131篇 |
国内免费 | 3660篇 |
出版年
2024年 | 45篇 |
2023年 | 241篇 |
2022年 | 356篇 |
2021年 | 434篇 |
2020年 | 424篇 |
2019年 | 461篇 |
2018年 | 288篇 |
2017年 | 311篇 |
2016年 | 329篇 |
2015年 | 460篇 |
2014年 | 653篇 |
2013年 | 564篇 |
2012年 | 782篇 |
2011年 | 717篇 |
2010年 | 597篇 |
2009年 | 601篇 |
2008年 | 665篇 |
2007年 | 639篇 |
2006年 | 567篇 |
2005年 | 501篇 |
2004年 | 372篇 |
2003年 | 326篇 |
2002年 | 266篇 |
2001年 | 258篇 |
2000年 | 263篇 |
1999年 | 165篇 |
1998年 | 96篇 |
1997年 | 94篇 |
1996年 | 53篇 |
1995年 | 50篇 |
1994年 | 35篇 |
1993年 | 29篇 |
1992年 | 37篇 |
1991年 | 47篇 |
1990年 | 42篇 |
1989年 | 51篇 |
1988年 | 31篇 |
1987年 | 31篇 |
1986年 | 39篇 |
1985年 | 20篇 |
1984年 | 21篇 |
1983年 | 20篇 |
1982年 | 29篇 |
1981年 | 17篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1975年 | 12篇 |
1965年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
在整理青海省蚤类标本中,发现长刺双蚤 Amphipsylla longispina Scalon, 1950一新亚种,记述如下。 长刺双蚤共和亚种 Amphipsylla longis pina gongheensis新亚种 鉴别特征 新亚种可动突前缘较直,不动突较细长,阳茎钩突端部似鸟头状; 相似文献
12.
Structural relatedness of lysis proteins from colicinogenic plasmids and icosahedral coliphages 总被引:4,自引:0,他引:4
The host-lysis-inducing functions of phi X174 protein E and MS2 protein L
were recently shown to reside on the N-terminal and C-terminal halves of
the two respective lysis proteins. In the present study it is shown that
the small lysis proteins encoded in various colicinogenic plasmids share
local sequence similarities and certain structural characteristics with the
essential peptides of their coliphage-coded counterparts. Despite their
dissimilar sizes and origins, it is suggested that the colicinogenic lysis
proteins are functionally analogous and evolutionarily related to those of
icosahedral single- stranded DNA and RNA phages.
相似文献
13.
An acid protease was purified from the mycelial form of Mucor rouxii by a method which involved salt and acid precipitation, gel filtration and anion-exchange chromatography. The enzyme had a molecular mass of 16,000 Da. Its optimum pH was 4.0, maximal activity was obtained at 50°C, and it was inactivated at 70°C. It was not affected by leupeptin or N -p-tosyl-L-lysine chloromethyl ketone (TLCK) but diazoacetyl-DL-norleucine methyl ester (DNME) in the presence of Cu2+ and more noticeably pepstatin A, strongly inhibited the activity. This acid protease did not activate zymogenic chitin synthetase from the fungus, but brought about its inactivation even at low concentrations and after short periods of incubation time.Abbreviations TLCK
N -p-tosyl-L-lysine chloromethyl ketone
- DNME
diazoacetyl-DL-norleucine methyl ester
- TCA
trichloroacetic acid
- SDS
sodium dodecyl sulfate 相似文献
14.
This article reports the effect of cold storage at 4 °C from December to April on chestnut cuttings. Rooting was found to
increase after four months preceded by treatment with 4000 mg l-1 IBA.
ThePhaseolus test of the biological activity of extracts of the cuttings showed the inhibition exerted by the acid fraction of the fresh
(December) cuttings to have been replaced by a rootpromoting effect in cuttings stored for 4 months at low temperature. Cold
storage thus seems to favour rooting. 相似文献
15.
本实验在14只麻醉开胸狗心脏上观察了氟碳乳剂与右旋糖酐稀释血液对心肌耗氧量与供应缺血心肌氧量关系的影响。以左室压力-时间指数(SPTI)作为心肌耗氧量的指标,根据冠脉有效侧支血流量(ECF)、PaO_2和 Hb 浓度计算供应缺血心肌的氧量。实验结果表明,低分子右旋糖酐稀释血液后,SPTI 暂时性轻度增加(稀释后30min 时较对照增加7.1±2.7%,P<0.05,稀释后60min 时增加2.8±1.2%,P>0.05),ECF 明显增多(稀释后30min 时较对照增加58.5±6.1%,P<0.01),缺血区边缘心肌氧供需关系未发生明显变化。氟碳乳剂稀释血液后,SPTI 的变化规律与右旋糖酐稀释后相同(稀释后30min 和60min 时分别较对照增加2.5±0.7%和1.9±0.8%)ECF 和 PaO_2升高(稀释后30min 时分别较对照增加53.9±6.7%和93±8.9%),供应缺血心肌的氧量显著增加,缺血区边缘心肌氧供需矛盾明显改善。 相似文献
16.
The 18p- syndrome. Report of five cases 总被引:2,自引:0,他引:2
R M Zumel M T Darnaude A Delicado A Diaz de Bustamante M L de Torres I López-Pájares 《Annales de génétique》1989,32(3):160-163
Five children, three males and two females were found to have a short arm deletion of chromosome 18. Four of them display some of the typical features of this syndrome: microcephaly, round face, hypertelorism, broad-based nose, "carp-mouth", microrethrognathia, pterygium colli, dysplastic and low set ears, clinodactily, failure to grow, muscular hypotony and mental retardation. Different hypotheses are discussed in order to explain the variable phenotypical expression of the 18 p-syndrome. 相似文献
17.
Phosphorylation of the gastric H,K-ATPase by Pi has been studied by measuring the P18Oj16O4-j distribution as a function of time at different H+, K+, and [18O]Pi concentrations. The advantage of isotope exchange measurements is that the P18Oj16O4-j distribution depends on the relative rates of HOH loss to form the phosphoenzyme intermediate and Pi dissociation from the enzyme. Therefore, 18O exchange is a sensitive probe of mechanism. K+ increases the exchange rate (v(ex] but does not affect the partition coefficient (Pc) that determines the P18Oj16O4-j distribution. Conversely, H+ inhibits exchange. A single Pc describes the data at every pH, but the value increases from 0.04 at pH 8 to 0.64 at pH 5.5. Vex depends hyperbolically on [Pi]0. Km for Pi does not depend on pH, and Pc does not depend on [Pi]0. Individual rate constants in the phosphorylation mechanism are estimated. Formation of the E.Pi complex that looses HOH is 1-2 orders of magnitude slower at pH 5.5 than at pH 8 and is not diffusion controlled. The observed change in Pc with pH is compatible with catalysis occurring by a different mechanism when a group with pKa = 7.2 is protonated. Slower than diffusion-controlled formation of the E.Pi complex that splits out HOH is evidence for a relatively slow, unimolecular chemical transformation involving an additional intermediate in the phosphorylation mechanism, such as a protein conformational change. 相似文献
18.
19.
Uranium-series dating of coral samples from raised marine terrace deposits between 1.5 and 10 m above sea level in the La Paz Peninsula area, Baja California Sur, yielded ages between 123 ka and 138 ka that are in agreement with previously reported results. The stratigraphy and ages of marine units near the El Coyote Arroyo indicate the presence of two high stands of the sea during the last interglacial or oxygen isotope substage 5e at about 140 ka and 123 ka. Accepting 5 m for the sea level during the last interglacial transgression, we calculate average uplift rates for the marine terraces of about 70 mm/ka and 40 mm/ka. These slow rates of uplift indicate a relative stability of the La Paz peninsula area for the past 140 000 years. In contrast, areas of Baja California affected by major faultf experienced higher rates of uplift. Rockwell et al. (1987) reported vertical uplift rates of 180 to 300 mm/ka at Punta Banda within the Aqua Blanea fault zone in northern Baja California. 相似文献
20.