全文获取类型
收费全文 | 70967篇 |
免费 | 5475篇 |
国内免费 | 130篇 |
出版年
2022年 | 511篇 |
2021年 | 1244篇 |
2020年 | 929篇 |
2019年 | 1138篇 |
2018年 | 1986篇 |
2017年 | 1685篇 |
2016年 | 2121篇 |
2015年 | 3052篇 |
2014年 | 3212篇 |
2013年 | 4234篇 |
2012年 | 4899篇 |
2011年 | 4492篇 |
2010年 | 3067篇 |
2009年 | 2561篇 |
2008年 | 3625篇 |
2007年 | 3369篇 |
2006年 | 3262篇 |
2005年 | 2892篇 |
2004年 | 2851篇 |
2003年 | 2554篇 |
2002年 | 2520篇 |
2001年 | 1692篇 |
2000年 | 1513篇 |
1999年 | 1373篇 |
1998年 | 818篇 |
1997年 | 705篇 |
1996年 | 616篇 |
1995年 | 588篇 |
1994年 | 458篇 |
1993年 | 505篇 |
1992年 | 844篇 |
1991年 | 821篇 |
1990年 | 734篇 |
1989年 | 677篇 |
1988年 | 565篇 |
1987年 | 524篇 |
1986年 | 508篇 |
1985年 | 577篇 |
1984年 | 515篇 |
1983年 | 418篇 |
1982年 | 333篇 |
1981年 | 344篇 |
1980年 | 309篇 |
1979年 | 399篇 |
1978年 | 353篇 |
1977年 | 355篇 |
1976年 | 342篇 |
1975年 | 335篇 |
1974年 | 327篇 |
1973年 | 317篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
91.
92.
Blanco Pablo J. Müller Lucas O. Watanabe Sansuke M. Feijóo Raúl A. 《Biomechanics and modeling in mechanobiology》2020,19(5):1663-1678
Biomechanics and Modeling in Mechanobiology - The goal of this work is to assess the impact of vascular anatomy definition degree in the predictions of blood flow models of the arterial network. To... 相似文献
93.
A cholinergic proteolipid fraction (i.e. a hydrophobic lipoprotein) was separated from the of the cow, using affinity chromatography with the lipophilic gel Sephadex LH-20 and p-phenyltrimethylamonium as the active group. High affinity binding studies showed that only the specific fraction, desorbed after an acetylcholine (or acid) pulse, and corresponding to 0,72% of the proteolipids, is the one that binds the cholinergic ligands. The binding of (3H)atropine and (14C)d-tubocurarine demonstrated that there are 814 picomoles/g fresh tissue of muscarinic sites and only 76 picomoles/g of nicotinic sites. The specific radioactivity for (3H)atropine is 10,000 nmoles/g protein, suggesting a high degree of purification of the specific cholinergic proteolipid. 相似文献
94.
Activation of the sympathetic system by phencyclidine (PCP) should result in catecholamine release from the adrenals. However, adrenalectomy does not reduce PCP-induced hypertension. In an attempt to rectify this inconsistency, the direct effects of PCP on the bovine adrenal medulla were examined. At (3×10?6M), PCP reduced the acetylcholine-(ACh)-induced catecholamine release by 50%. Surprisingly, barium-induced secretion of catecholamines was also reduced by PCP. ACh-induced catecholamine release was not altered by 10?3M 4-aminopyridine (4 AP), the potassium channel blocker. Thus, calcium antagonist actions of PCP and consequent block of catecholamine secretion from adrenal medulla may explain the lack of effect of adrenalectomy on PCP-induced hypertension. Possible contributions of calcium and/or potassium channel blockade to other manifestations of PCP overdosage are discussed. 相似文献
95.
Francisco E. Fontúrbel 《Mammalian Biology》2010,75(4):294-301
Assessing small mammal diversity is a common procedure, which usually employs widespread standard techniques, for gathering information for a wide range of studies. Traditional methods, however, may be biased against capturing arboreal marsupials, such as Dromiciops gliroides, an endemic marsupial currently considered a rare species in the Patagonian temperate rainforest due to the low abundances reported previously. I tested a new capturing methodology to assess the small mammal diversity of an old-growth forest in Patagonia, based on a randomized and balanced design, which incorporated a combination of different trap types, bait types, and placement heights. The proposed methodology included four trap types (two for live-capturing: wire-mesh and Sherman traps, and two sign-recording traps for tracks and hair), two types of bait (banana and rolled oats), and two trap placements (ground level and 1.5–2.5 m above the ground). Trap type, bait type, and height of placement all had significantly different effects on capturing and detecting rodents or marsupials; environmental variables at the trap location also affected the ability to detect rodents and marsupials. Traditional methods used for sampling small mammals performed well for rodents but are not effective for capturing marsupials and vice versa, showing species-specific sampling protocols. There is no single combination of trap-bait-height capable to assess the entire small mammal community, but the combination of the most effective protocol for rodents and the most effective protocol for marsupials guarantee better results. 相似文献
96.
97.
Ildikó Vidra Kálmán Simon László Institóris Ingeborg Csöregh Mátyás Czugler 《Carbohydrate research》1982,111(1):41-57
After hydrolysis of 1,6-dibromo-1,6-dideoxygalactitol (1) and 1,2:5,6-dianhydrogalactitol (2), 11 compounds were isolated, three of them as tritylated derivatives. Their structures were established on the basis of chemical evidence and, for four compounds, by X-ray diffraction. The main product of the hydrolysis of 1 was 3,6-anhydro-1-bromo-1-deoxy-dl-galactitol; the end-products of the hydrolysis of 2 were 1,5-anhydro-dl-galactitol, 2,5-anhydro-dl-altritol, and galactitol. 相似文献
98.
99.
Siddhartha Kumar Bhaumik Manoj Kumar Singh Subir Karmakar Tripti De 《Glycoconjugate journal》2009,26(6):663-673
As compared to cutaneous leishmaniasis, vaccination against visceral leishmaniasis (VL) has received limited attention. In
this study, we demonstrate for the first time that an UDP-Galactose: N-acetylglucosamine β 1–4 galactosyltransferase (GenBank Accession No. EF159943) expressing attenuated LD clonal population (A-LD) is able to confer protection against the experimental challenge with the virulent LD AG83 parasite. A-LD was also effective in established leishmania infection. The vaccinated animals showed both cell mediated
(in vitro T-cell proliferation, and DTH response) and humoral responses (Th1 type). These results demonstrate the potential of the
attenuated clones as an immunotherapeutic and immunoprophylactic agent against visceral leishmaniasis. 相似文献
100.
In the River Lobos-Ucero and its tributary the River Avión-Milanos (Duero basin, Old Castile, Central Spain), two limestone streams fed by aquifers, the population of brown trout, as compared with the populations of other European streams, shows a high growth rate, high condition coefficients, short life-span and early age at first maturity. Gonad cycle was also studied. Size distributions of unshed eggs exhibit a dynamic activity with a bi-modal distribution from June onwards, spawning occurred in the last days of November. Fecundity (F) can be predicted from trout length (L, mm) according to the equation: F= –646.47+5.6167 · L. Numbers and standing crop of trout range from 18 to 3903 ind. ha–1 and 3.6 to 452.9 Kg ha–1, reaching higher values in the sites close to the aquifers. Egg production had values of 22.4 and 18.0 eggs m–2 in the Rivers Ucero and Avión-Milanos respectively. Some factors suggested as regulators of these demographical characteristics are discussed in the light of recent literature. 相似文献