全文获取类型
收费全文 | 1593篇 |
免费 | 152篇 |
国内免费 | 191篇 |
专业分类
1936篇 |
出版年
2024年 | 6篇 |
2023年 | 25篇 |
2022年 | 30篇 |
2021年 | 72篇 |
2020年 | 68篇 |
2019年 | 74篇 |
2018年 | 56篇 |
2017年 | 63篇 |
2016年 | 59篇 |
2015年 | 53篇 |
2014年 | 81篇 |
2013年 | 143篇 |
2012年 | 67篇 |
2011年 | 87篇 |
2010年 | 81篇 |
2009年 | 84篇 |
2008年 | 87篇 |
2007年 | 83篇 |
2006年 | 79篇 |
2005年 | 69篇 |
2004年 | 65篇 |
2003年 | 52篇 |
2002年 | 47篇 |
2001年 | 35篇 |
2000年 | 37篇 |
1999年 | 37篇 |
1998年 | 46篇 |
1997年 | 37篇 |
1996年 | 30篇 |
1995年 | 20篇 |
1994年 | 27篇 |
1993年 | 20篇 |
1992年 | 22篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有1936条查询结果,搜索用时 15 毫秒
91.
92.
Immobilised activated sludge based biosensor for biochemical oxygen demand measurement 总被引:5,自引:0,他引:5
A biochemical oxygen demand (BOD) sensor, based on an immobilised mixed culture of microorganisms in combination with a dissolved oxygen electrode, has been developed for the purpose of on-line monitoring of the biological treatment process for waste and wastewater. The sensor was designed for easy replacement of the biomembrane, thereby making it suitable for short-term use. The drawbacks of activated sludge based sensor, such as short sensor lifetime, were thereby circumvented. The sensor BOD measurements were carried out in the kinetic mode using a flow injection system, resulting in 25 s for one measurement followed by 4–8 min recovery time. Based on the results of normalised sensor responses, the OECD synthetic wastewater was considered to be a more suitable calibration solution in comparison with the GGA solution. Good agreement was achieved between the results of the sensor BOD measurement and those obtained from BOD5 analysis of a wastewater sample from a food-processing factory. Reproducibility of responses using one sensor was below ±5.6% standard deviation. Reproducibility of responses using different sensors was within acceptable bias limits, viz. ±15% standard deviation. 相似文献
93.
Allozyme electrophoresis of four sibling parthenogenetic Caucasian rock lizards Darevskia unisexualis, D.uzzelli, D.sapphirina, and D.bendimahiensis found seven clones and five variable loci. The data supported the hypothesis that D.raddei and D.valentini are the parental species of all four parthenogens. Variation patterns in Darevskia were summarized. Species that originated from a single F1 typically consisted of one widespread clone with a few rare clones. Species with multiple origins displayed variation only
slightly higher than species with a single origin. This is contrary to other genera of parthenogenetic lizards, in which cases
massive clonal variations were observed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
94.
F. Bangerth 《Plant Growth Regulation》2000,31(1-2):43-59
Natural abscission of young fruit and its regulation by plant hormones isconsidered and compared to the generally accepted model of senescencetriggered abscission of, for example, leaves or mature fruit. It isconcluded that abscission of young fruit cannot be explained by this model.Alternatively, it is suggested that the senescence triggered initial step inthe classical abscission model should be replaced by a correlativelytriggered step. Polar basipetal IAA transport with its autostimulation andautoinhibition components is the main regulating signal in this correlativeacting system and replaces ethylene as the initial driving force from thesenescence triggered model.Results supporting this model are presented and tested against existingresults from the literature. Finally, this hypothesis is tested as a possibleexplanation of the mode of action of some thinning chemicals orbioregulators. It is speculated how a thinning chemical should be designedto function in a more reliable way, at least as far as its interference with the endogenous hormone system is concerned. 相似文献
95.
Age, growth, and reproductive biology of the blackbelly rosefish from the Carolinas, U.S.A. 总被引:1,自引:0,他引:1
Otoliths and gonads of blackbelly rosefish Helicolenus dactylopterus dactylopterus were collected from the commercial fishery off the Carolinas in 1994–1997. Opaque bands on transverse sections of otoliths were determined to be annuli by analysis of marginal increments. Opaque zone formation occurs between July and January. Ages ranged from 7 to 30 years. Blackbelly rosefish have intraovarian gestation. Fertilization is internal, as free spermatozoa were found primarily in resting ovaries from July through early December with peak occurrence in September through November. There was a delay of 1–3 months before fertilization, as oocyte development did not begin until December. Occurrence during January through April of early-celled embryos, the most advanced stage observed, and postovulatory follicles indicated that oocyte development was rapid. Egg development occurs in a clear gelatinous matrix secreted into the ovarian cavity. The reproductive mode is a zygoparous form of oviparity, intermediate between oviparity and viviparity. Population sex ratio departed markedly from 1: 1 for most length intervals. Males were more abundant at lengths >250 mm L T and the overall male: female ratio was 1 : 0·60. 相似文献
96.
97.
The exact timing ofAnguilla japonica spawning was determined from analyses of daily otolith increments in leptocephali collected near a spawning area west of
the Mariana Islands on July 1–18, 1991. The birth dates of the 54 leptocephali examined (10.2 to 30.5 mm in total length)
ranged from May 22 to June 24, 1991, the individuals clearly comprising two age groups, May-born fish (mode May 28) and June-born
fish (mode June 21). The data showed thatA. japonica spawns intermittently during the spawning season, with fixed synchronized timing. Each group of leptocephali collected along
three different north-south transects (131°, 134° and 137°E between 10° and 22°N) comprised both May-born and June-born fish.
The latter were dominant along the easternmost and middle transects, whereas the May-born fish were more abundant along the
westernmost transect. The modal ages of the June-born and May-born fish collected along 137°E on July 1–3 were 13 d and 35
d, respectively, while those of the two age groups collected along 134°E on July 17 and 18 were 28 d and 50 d, respectively.
These data show that the interval between the sampling dates for the two transects (ca. 15 d) corresponded closely to the
differences in modal ages of specimens from the two transects (15 d) for both the May- and June-born fish, and further, that
the difference in modal age between the two age groups (22 d) was the same at both transects. A similar correspondence in
total length was also observed between the two age groups at the above two transects. The findings clearly demonstrated parallel
westward transport by the North Equatorial Current for both the May- and June-born eel leptocephali, which originated from
a spawning area estimated as being between 141° and 143°E. 相似文献
98.
Eric Hanssen Suzanne Franc Robert Garrone 《Biology of the cell / under the auspices of the European Cell Biology Organization》1998,90(3):223-228
A central issue in the understanding of Marfan syndrome deals with the functional architecture of fibrillin-containing microfibrils. Fibrillin-rich microfibrils are long extracellular matrix fibrillar components exhibiting a 50 nm periodic beaded-structure with a width of around 20–25 nm after rotary shadowing and a 10–12 nm diameter when observed in ultra-thin sections. They are composed of fibrillin monomers more or less associated with many other components which are, for the most part, poorly characterized up to date. They are known to be elastic but few data have been accumulated to understand their properties. Atomic force microscopy (AFM) allowed us to morphologically differentiate fibrillin-rich microfibrils from other fibrillar components and to investigate the thin structure of these beaded filaments in their native state. They showed, in AFM, a periodic beaded structure ranging from 50 to 60 nm and a width of about 40 nm. The different sizes of fibrillin-containing microfibrils previously observed after rotary shadowing and in ultra-thin sections was resolved with our technique and is revealed to be 10 nm in diameter. Each beaded microfibril appears to be composed of heterogeneous beads connected by 2–3 arms. An orientation of the microfibrils has been shown, and allows us to propose a complementary model of microfibrillar monomer association. 相似文献
99.
100.
《Bioorganic & medicinal chemistry》2014,22(23):6684-6693
A series of (R)-3-amino-1-((3aS,7aS)-octahydro-1H-indol-1-yl)-4-(2,4,5-trifluorophenyl)butan-1-one derivatives was designed, synthesized, and evaluated as novel inhibitors of dipeptidyl peptidase-4 (DPP-4) for the treatment of type 2 diabetes. Most of the synthesized compounds demonstrated good inhibition activities against DPP-4. Among these, compounds 3e, 4c, 4l, and 4n exhibited prominent inhibition activities against DPP-4, with IC50s of 0.07, 0.07, 0.14, and 0.17 μM, respectively. The possible binding modes of compounds 3e and 4n with dipeptidyl peptidase-4 were also explored by molecular docking simulation. These potent DPP-4 inhibitors were optimized for the absorption, distribution, metabolism, and excretion (ADME) properties, and compound 4n displayed an attractive pharmacokinetic profile (F = 96.3%, t1/2 = 10.5 h). 相似文献