全文获取类型
收费全文 | 70452篇 |
免费 | 4703篇 |
国内免费 | 6篇 |
出版年
2023年 | 521篇 |
2022年 | 433篇 |
2021年 | 942篇 |
2020年 | 873篇 |
2019年 | 862篇 |
2018年 | 2281篇 |
2017年 | 2081篇 |
2016年 | 2653篇 |
2015年 | 3343篇 |
2014年 | 3310篇 |
2013年 | 4620篇 |
2012年 | 5579篇 |
2011年 | 5170篇 |
2010年 | 3146篇 |
2009年 | 2353篇 |
2008年 | 4018篇 |
2007年 | 3746篇 |
2006年 | 3523篇 |
2005年 | 2997篇 |
2004年 | 2953篇 |
2003年 | 2648篇 |
2002年 | 2429篇 |
2001年 | 1684篇 |
2000年 | 1742篇 |
1999年 | 1228篇 |
1998年 | 536篇 |
1997年 | 400篇 |
1996年 | 407篇 |
1995年 | 375篇 |
1994年 | 314篇 |
1993年 | 297篇 |
1992年 | 581篇 |
1991年 | 507篇 |
1990年 | 433篇 |
1989年 | 421篇 |
1988年 | 423篇 |
1987年 | 381篇 |
1986年 | 349篇 |
1985年 | 374篇 |
1984年 | 361篇 |
1983年 | 257篇 |
1982年 | 240篇 |
1981年 | 184篇 |
1980年 | 188篇 |
1979年 | 228篇 |
1978年 | 219篇 |
1975年 | 208篇 |
1974年 | 228篇 |
1973年 | 233篇 |
1972年 | 189篇 |
排序方式: 共有10000条查询结果,搜索用时 797 毫秒
991.
I Martín de Miranda J C Macome L E Costa A C Taquini 《Acta physiologica latino americana》1977,27(2):65-71
The role of the gonads and their hormones on body weight was studied in rats of both sexes submitted to chronic hypoxia and their controls at sea level atmospheric pressure. Intact rats were exposed to either 4 700 or 6 000 m simulated altitude in a hypopressure chamber. Castrated rats and castrated rats daily injected with either 0.5 mg of testosterone or 20 microgram of estradiol or the vehicle, were exposed to the higher altitude. The rat weight was recorded for a period of at least eight weeks. All groups of hypoxic male animals increased their weight significantly less than the controls at sea level. Also in castrated females and in castrated injected with testosterone or the vehicle the same pattern of weight curves was observed. On the contrary, groups of intact females and castrated females injected with estradiol did not show significant differences between hypoxic and control animals. Only in a group of smaller intact females (50-80 g) the body weight increase was significantly diminished by exposure to either 4 700 or 6 000 m simulated altitude. 相似文献
992.
Jan Jeník 《Folia Geobotanica》1977,12(2):208-208
993.
Bubeník J. Perlmann P. Indrová M. Šimová J. Jandlová T. Neuwirt J. 《Cancer immunology, immunotherapy : CII》1983,14(3):205-206
Summary Supernatants from Con A-stimulated rat spleen cell cultures containing T cell growth factor inhibited growth of a transplantable 3-methylcholanthrene-induced sarcoma in syngeneic mice. The tumour-inhibitory effects were dependent on the concentration of T cell growth factor and repeated injections of the supernatants. 相似文献
994.
Cyclopiazonic acid is a toxic metabolite of fungal origin that inhibits protein synthesis in intact HeLa cells and eukaryotic cell-free systems. It has been shown that cyclopiazonic acid blocks the GTP- and EF-1-dependent binding of (3H)Phe-tRNA to 80S ribosomes. Moreover the translocation of N-Ac-(3H)Phe-tRNA by 80S ribosomes that takes place in the presence of EF-2 and GTP is also halted by cyclopiazonic acid. It is concluded that this drug affects a ribosomal site involved in the alternative interaction of elongation factors EF-1 and EF-2. 相似文献
995.
In female rats aged 21 and 80 days, uninephroadrenalectomy with enucleation of the remaining adrenal was performed and 0.17 mol X l-1 saline offered as the only drinking fluid. The changes of plasma concentration of renin (PRC), and its substrate (RSC) and renal renin activity (RRA), considered as an indicator of the secretory activity of the regenerating adrenal were studied 5, 10, 20, 40 and 60 days after the adrenal enucleation to look for possible age differences related to the higher susceptibility of immature rats to the hypertensive influence of the regenerating adrenal. It has been found that: 1. In adrenal-enucleated rats the saline-induced decrease of RRA was delayed for a shorter time period in immature rats than in adult ones (5 vs. 10 days), during which blood pressure, saline consumption and RSC were lowered. The decrease of PRC was retarded in the older group only. 2. In rats with regenerating adrenals the PRC and RRA decrease was greater in animals subjected to enucleation of the remaining adrenal gland when immature, than in those operated when adult. At the end of the experiment this age difference disappeared. 3. The age difference in PRC and RRA suppression appeared during the period, when neither blood pressure nor saline consumption were higher in immature rats than in adult ones. 4. In rats with regenerating adrenals the renal mass was greater than in saline drinking controls. In the younger group, which in contrast to the adult one developed hypertension, this increase was greater and directly related to the blood pressure level from the 20th post-enucleation day onwards. It is being suggested that the changes of PRC, RRA and RSC observed up to the 10th post-enucleation day indicates relative adrenal insufficiency, the shorter duration of which in immature rats reflects their higher sensitivity to mineralocorticoids produced by the regenerating adrenal. This also manifests itself by greater PRC and RRA suppression in this age group. The haemodynamic results of the greater RRA suppression in the not yet fully developed kidneys of immature rats may facilitate the development of a "vicious circle" mechanism between blood pressure and hypertensive renal damage and thus contribute to the higher sensitivity to adrenal-regeneration hypertension. 相似文献
996.
Juan Ortín Concepción Martínez Lucía del Río Mercedes Dávila Cecilio López-Galíndez Nieves Villanueva Esteban Domingo 《Gene》1983,23(2):233-239
The complete genetic information contained in the influenza virus RNA segment 7 of the A/Bangkok/ (H3N2) strain has been cloned by in vitro synthesis of the complementary dsDNA and its insertion into plasmid pBR322. The nucleotide sequence of the viral RNA segment has been determined from the cDNA insert. It is 1027 nucleotides long, and contains two open reading frames, as shown for other influenza virus strains. When compared with the previously published sequence for the A/Udorn/72 (H3N2) strain, 15 nucleotide exchanges are observed, most of them silent mutations, and only two causing amino acid changes in each of the M1 and M2 protein sequences. 相似文献
997.
Thylakoid membranes of the cyanobacterium Plectonema boryanum solubilized with Triton X-100 can be resolved into three fractions of pigment-protein complexes (Hladík, J. and Sofrová, D. (1981) Photosynthetica 15, 490–503). Fraction I contained relatively the highest amount of carotenoids as well as monomeric forms of chlorophyll a, Fractions II and III contained chlorophyll-protein complexes with a characteristic exciton-split circular dichroism in the red region. It has been shown that fraction III is an oligomeric form of the chlorophyll-protein complex of fraction II. Circular dichroism spectra indicate that, different from fraction II, fraction III contains specifically oriented and space-fixed molecules of carotenoids. Thermal dissociation of fracion III to fraction II is accompanied by disappearance of the positive circular dichroism effect of carotenoids in the 500–550 nm region, thus causing deorganization of the carotenoids, proceeding in parallel to the geometrical rearrangement of chlorophyll molecules. Extraction of the carotenoids of fraction III with heptane is acompanied by dissociation of fraction III. We assume that the observed effects are due to binding of the two pigments to the protein component of the complex and that carotenoids can mediate a part of the interactions which stabilize the structure of pigment-protein complexes. Thus, besides the light-harvesting and protective functions, carotenoids can also play a structural role. 相似文献
998.
I. Michalík 《Biologia Plantarum》1982,24(3):161-169
In an experiment with native maize roots depending on different phosphorus concentration in the external solution (0.001 …
50 mM P), the multiphasic character of the kinetics of phosphate uptake has been stated. The single phases are characterized
by the different values of Km and Vmax. In the wide range of concentrations the isotherm of the phosphate uptake has five evident phases. The character of kinetics
for the uptake of phosphate is analogical to the kinetics of the enzymatic reactions described by the Michaelis-Menten equation.
On the other hand the linear dependence for the inactivated root was determined,i.e. the uptake of phosphate versus different phosphorus concentration in the external solution.
The graphic representation of the logarithmic values for the phosphorus taken up versus the different phosphorus concentration
in the external solution gives the biphasic course including concentration less than 1.0 mM P and more than 1.0 mM P. Within
the framework of the concentration range the following values of Vmax, Km and ϕin were calculated under the conditions if the concentration of phosphorus is less than 1.0mMP: Vmax = 1.705 μmol P × g-1h-1, Km = 0.057 mM P and ϕin = 0.83,i.e. if the concentration of phosphorus is more than 1.0mM P: Vmax = 40 μmol P × g-1 h-1, Km = 16.66 mM and ϕin = 20.
According to these results, the phosphate concentration in the external solution influences the activity of the transport
mechanisms concerning their conformative changes which discretely change their working regime of membrane transport. This
is also demonstrated in the change of values Vmax, Km and ϕin. 相似文献
999.
1000.
Responses of the epidermal diffusive conductance (gep) to irradiance (I) during ontogeny of primary bean leaves or during their wilting were followed. Effects ofI, leaf age and leaf water potential (Ψw) as well as interactive effects (I × leaf age andI × Ψw) ongep were statistically significant. 相似文献