全文获取类型
收费全文 | 11689篇 |
免费 | 723篇 |
专业分类
12412篇 |
出版年
2023年 | 63篇 |
2022年 | 66篇 |
2021年 | 148篇 |
2020年 | 131篇 |
2019年 | 131篇 |
2018年 | 324篇 |
2017年 | 300篇 |
2016年 | 361篇 |
2015年 | 518篇 |
2014年 | 560篇 |
2013年 | 747篇 |
2012年 | 1063篇 |
2011年 | 1546篇 |
2010年 | 779篇 |
2009年 | 764篇 |
2008年 | 543篇 |
2007年 | 517篇 |
2006年 | 446篇 |
2005年 | 425篇 |
2004年 | 396篇 |
2003年 | 362篇 |
2002年 | 344篇 |
2001年 | 323篇 |
2000年 | 302篇 |
1999年 | 251篇 |
1998年 | 76篇 |
1997年 | 50篇 |
1996年 | 48篇 |
1995年 | 40篇 |
1994年 | 39篇 |
1993年 | 34篇 |
1992年 | 79篇 |
1991年 | 81篇 |
1990年 | 67篇 |
1989年 | 56篇 |
1988年 | 54篇 |
1987年 | 42篇 |
1986年 | 35篇 |
1985年 | 41篇 |
1984年 | 39篇 |
1983年 | 25篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 18篇 |
1979年 | 18篇 |
1977年 | 15篇 |
1975年 | 13篇 |
1973年 | 10篇 |
1972年 | 10篇 |
1968年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Summary Two extra bisatellited chromosome identified as inv dup (15) (pterq11.2::q11.2pter) were found in an oligoasthenospermic male. Analysis of Ag-staining in the proband and in one fertile brother with a normal karyotype revealed that nucleolar organizer region (NOR) activity was significantly increased in the patient. The frequency of satellite associations was also significantly higher in the index case, but no correlation was found between NOR activity and acrocentric associations. These results suggest that extra NOR activity and the elevated frequency of satellite associations could predispose to gametogenic impairment. 相似文献
52.
Chromosome pairing in females and males of diploid (2n = 22) and tetraploid (2n = 44) Odontophrynus americanus and diploid Ceratophrys cranwelli (2n = 26) and tetraploid C. ornata (2n = 104) showed that diploid females formed more chiasmata per paired arm than diploid males and polyploids of both sexes. There was a reduction in the level of recombination in female polyploids by forming multivalents with terminal chiasmata. The reduction reflected a change in the genetic control of pairing in females after polyploidization. 相似文献
53.
54.
55.
56.
The photoperiodic variations of testosterone plasmatic levels in male rabbits have been studied. The animals were subjected to the influence of three circadian rhythms: 12/12, 14/10 and 10/14 h of light/darkness. The hormone assay was carried out using an enzymeimmunoassay method (Competitive ELISA). Blood samples were of two different types: seriated and non-seriated, to find if these might be any differences in the results. It is concluded that testosterone plasmatic levels are within physiologic values (0.3-10.0 ng/ml), although differences depending on the light/darkness cycle and on the type of blood extraction are remarkable; for this reason the selection of the circadian rhythm will depend on the experimentation that is to be carried out. 相似文献
57.
R González-Cámpora C Otal-Salaverri P Panea Flores A Hevia-Vázquez A Gómez Pascual V San Martín Díez 《Acta cytologica》1992,36(2):152-158
Peripheral neuroepithelioma of soft tissue is a malignant primitive neuroectodermal tumor that appears both in children and adults and usually has a poor outcome. Fine needle aspiration on two patients with tumors in the lower limbs showed small round cells with unipolar processes and a tendency to form Homer-Wright rosettes. The cells had a round to oval nucleus with fine chromatin, up to four small, conspicuous nucleoli and vacuolated, periodic acid-Schiff-positive cytoplasm. The diagnosis was supported by electron microscopic study of the aspirate, which showed features of neuroblastic differentiation (i.e., neurosecretory granules), and by histologic, immunohistochemical and cytogenetic study of the resected tumors. 相似文献
58.
The Na+/Ca2+ exchanger of squid axons, barnacle muscle and sarcolemma requires micromolar intracellular calcium for activation in the Na+i/Ca2+o exchange mode ('reverse' Na+/Ca2+ exchange). The requirement for [Ca2+]i has been demonstrated with the use of intracellular calcium buffers, such as Quin-2, to inhibit Na+i/Ca2+o exchange. However, the inhibition of Na+i/Ca2+o exchange in mammalian nerve terminals loaded with Quin-2 has not been observed [7], suggesting a lower sensitivity to low [Ca2+]i for this system. In contrast, the results reported herein indicate that 45Ca2+ uptake in synaptosomes through Na+i/Ca2+o exchange is inhibited by Quin-2 much in the same way as it is in the squid, provided that synaptosomes are preincubated in low Ca2+ medium to avoid saturation of Quin-2. Under these conditions, 45Ca2+ efflux via Ca2+i/Ca2+o exchange is also inhibited. Our results indicate that the Na+i/Ca2+o and Ca2+i/Ca2+o modes of the Na+/Ca2+ exchanger from rat brain synaptosomes require intracellular calcium for activation. However, because no clear relationship between the observed [Ca2+]i values and the inhibition of Na+i/Ca2+o exchange has been found, it is suggested that localised submembrane calcium concentrations not detected by the [Ca2+]i probe might regulate the exchanger. 相似文献
59.
Francisco Guillén Angel T. Martinez Maria Jesús Martínez 《Applied microbiology and biotechnology》1990,32(4):465-469
Summary Production of extracellular hydrogen peroxide by fungal oxidases is been investigated as a requirement for lignin degradation. Aryl-alcohol oxidase activity is described in extracellular liquid and mycelium ofPleurotus eryngii and studied under non-limiting nitrogen conditions. This aryl-alcohol oxidase catalyses conversion of primary aromatic alcohols to the corresponding aldehydes and H2O2, showing no activity with aliphatic and secondary aromatic alcohols. The enzyme is stable at pH 4.0–9.0, has maximal activity at 45°–50°C and pH 6.0–6.5, is inhibited by Ag+, Pb2+ and NaN3, and has aK
m
of 1.2 mM using veratryl alcohol as substrate. A single protein band with aryl-alcohol oxidase activity was found in zymograms of extracellular and intracellular crude enzyme preparations fromP. eryngii. 相似文献
60.
Manuel Valmaseda Gonzalo Almendros Angel T. Martínez 《Applied microbiology and biotechnology》1990,33(4):481-484
Summary The ability of 45 fungal strains to degrade wheat straw and beech wood was studied. Degradation patterns were defined in terms of chemical evolution of substrates and changes in lignin and polysaccharides. Trametes versicolor produced an important degradation of lignin and increased substrate digestibility, but it caused high weight losses and gave rise to similar decay patterns on both substrates. A preferential degradation of lignin was produced during straw transformation by Pleurotus eryngii. The increase of soluble lignin and decreases of lignin content and H/C ratio defined the degradation tendency after principal component analysis. The cation exchange capacity and water and alkali solubility presented the highest loading factors for the characterization of fungal transformation of beech wood.
Offprint requests to: A. T. Martínez 相似文献