全文获取类型
收费全文 | 547359篇 |
免费 | 53920篇 |
国内免费 | 262篇 |
专业分类
601541篇 |
出版年
2018年 | 9837篇 |
2017年 | 9496篇 |
2016年 | 9734篇 |
2015年 | 8445篇 |
2014年 | 9769篇 |
2013年 | 13633篇 |
2012年 | 17219篇 |
2011年 | 21705篇 |
2010年 | 15778篇 |
2009年 | 14834篇 |
2008年 | 19271篇 |
2007年 | 21063篇 |
2006年 | 14074篇 |
2005年 | 14199篇 |
2004年 | 13948篇 |
2003年 | 13407篇 |
2002年 | 13032篇 |
2001年 | 20805篇 |
2000年 | 20695篇 |
1999年 | 16388篇 |
1998年 | 5883篇 |
1997年 | 6120篇 |
1996年 | 5668篇 |
1995年 | 5297篇 |
1994年 | 5144篇 |
1993年 | 5235篇 |
1992年 | 13521篇 |
1991年 | 13449篇 |
1990年 | 13220篇 |
1989年 | 12661篇 |
1988年 | 12112篇 |
1987年 | 11655篇 |
1986年 | 10837篇 |
1985年 | 10656篇 |
1984年 | 8975篇 |
1983年 | 7757篇 |
1982年 | 5930篇 |
1981年 | 5331篇 |
1979年 | 8577篇 |
1978年 | 6794篇 |
1977年 | 6240篇 |
1976年 | 6006篇 |
1975年 | 6573篇 |
1974年 | 7366篇 |
1973年 | 7285篇 |
1972年 | 7234篇 |
1971年 | 6506篇 |
1970年 | 5419篇 |
1969年 | 5390篇 |
1968年 | 5125篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
991.
Phenylacetic, 3-phenylpropionic, -hydroxyphenylacetic and 3 (-hydroxyphenyl) propionic acids together with the series of C2 to C6 saturated fatty acids previously reported in the anal sac secretion of the red fox () are identified as constituents of the anal sac secretion of the lion (Panthera leo). All these compounds are also observed in the anal sac secretion of the red fox using gas chromatography. The aerobic microflora of red fox and domestic dog () anal sac secretion samples invariably consisted predominantly of and . The hypothesis that the secretion volatiles so far identified may be microbiologically produced is examined. 相似文献
992.
993.
F. Fontaine E. Kiefer C. Clément M. Burrus J. L. Druelle 《Trees - Structure and Function》1999,14(2):83-90
In the present work, we described the fate of proventitious epicormic buds on the trunks of 40-year-old Quercus petraea trees and in parallel the vascular trace they produced in the wood. Our results show that small and large individual epicormic
buds can survive as buds for 40 years and that both are composed of a terminal meristem and scales. Meristematic areas are
detected in the scale axils of small buds; in addition to these meristems the large buds also have secondary bud primordia.
The small buds are connected to the pith of the main stem by a unique trace, whereas the large buds are connected by one or
multiple traces. A single trace might imply that the whole bud is still alive and multiple traces might indicate that the
terminal meristem has died. In the latter case, each trace is connected to a secondary bud of the large bud. The buds found
in a cluster are composed of a terminal meristem and scales with axillary meristems in the scale axils. A cluster is connected
to the pith of a stem either by a unique trace when it seems to be the result of partial abscission of an epicormic shoot
or multiple traces when it might have originated from an epicormic bud in which the terminal meristem has died. Whatever the
type of the bud, the vascular trace in the bark is composed of a cambium, secondary xylem and parenchyma cells and the trace
present in the wood had parenchyma cells with vestiges of secondary xylem. Each year, the vascular trace should be produced
in the bark by the cambium of the tree but not by the bud itself. On 40-year-old Q. petraea, we observed a proliferation of epicormic buds and in parallel a multiplication of the number of vascular traces in the trunk,
but the knots caused by the traces of epicormic buds in the wood, either as individuals or in clusters, are minor since their
colours are only slightly darker than those of woody rays and they are less than 2 mm in diameter. The knots will appear when
epicormic buds develop into shoots.
Received: 30 March 1999 / Accepted: 09 June 1999 相似文献
994.
A. V. Timofeev 《Plasma Physics Reports》2003,29(8):683-687
The conditions under which the energy of the electron Langmuir oscillations can escape from the plasma into vacuum are determined in the simplest model of a plane slab of an inhomogeneous cold magnetized plasma in a uniform magnetic field. 相似文献
995.
G Cavicchioni K Varani S Niccoli O Rizzuti S Spisani 《The journal of peptide research》1999,54(4):336-343
The formyltetrapeptides for-Met-Leu-Leu-Phe-OMe 1, for-Met-Leu-Aib-Phe-OMe 2, for-Met-Leu-Ac6c-Phe-OMe 3, for-Met-Leu-Pro-Phe-OMe 4, for-Met-Pro-Pro-Phe-OMe 5, for-Met-Aib-Aib-Phe-OMe 6, for-Met-Pro-Aib-Phe-OMe 7 and for-Met-Aib-Pro-Phe-OMe 8 were synthesized and biologically tested on human neutrophils in an attempt to evaluate the specific receptor pocket dimensions and features. Our results indicate that the shift in the Phe residue to the fourth position in these compounds strongly reduces chemotactic response, but is efficacious in triggering superoxide anion production and lysozyme release (order of potency 3 > 2 > 1 > 4 > 6 > 8 > 5 > 7). The potency of the two latter responses correlates well with the affinity data obtained in binding experiments. 相似文献
996.
M J Litzinger D E Brenneman 《Biochemical and biophysical research communications》1984,124(3):979-987
[3H] Nitrendipine binding was partially blocked by the presence of tetrodotoxin in developing spinal cord neurons. In young cultures, 1 micron tetrodotoxin displaced 29% and 26% of [3H] nitrendipine binding from the high and low affinity binding sites, respectively. In one month old cultures, tetrodotoxin had no effect on [3H] nitrendipine binding. The interaction between tetrodotoxin and nitrendipine in young cultures suggests ligand binding site similarities during development. 相似文献
997.
E A Ivanova 《Ontogenez》1987,18(3):320-323
The influence of testosterone on the rate of total protein synthesis in the reproductive tract tissues and muscles was studied in the guinea pig male embryos from 26 days of development until birth. The rate of protein synthesis was estimated by the intensity of 3H-leucine incorporation per 1 mg protein for 30 min. Testosterone increased the rate of protein synthesis at all studies stages. A higher rate of protein synthesis was revealed at the stages of active morphogenesis and growth of rudiments and organs of genital system and correlated with their ability of 3H-testosterone uptake (Ivanova, 1982). 相似文献
998.
Binding of ADP to beef-heart mitochondrial ATPase (F1) 总被引:1,自引:0,他引:1
1. ADP binding to beef-heart mitochondrial ATPase (F1), in the absence of Mg2+, has been determined by separating the free ligand by ultrafiltration and determining it in the filtrate by a specially modified isotachophoretic procedure. 2. Since during the binding experiments the 'tightly' bound ADP (but not the ATP) dissociates, it is necessary to take this into account in calculating the binding parameters. 3. The binding data show that only one tight binding site (Kd about 0.5 microM) for ADP is present. 4. It is not possible to calculate from the binding data alone the number of or the dissociation constants for the weak binding sites. It can be concluded, however, that the latter is not less than about 50 microM. 相似文献
999.
A method of retaining phloroglucinol proof of lignin 总被引:2,自引:0,他引:2
E O Speer 《Stain technology》1987,62(4):279-280
1000.
D. Y. Sorokin E. N. Detkova G. Muyzer 《Extremophiles : life under extreme conditions》2010,14(1):71-77
Evidence on the utilization of simple fatty acids by sulfate-reducing bacteria (SRB) at extremely haloalkaline conditions are practically absent, except for a single case of syntrophy by Desulfonatronum on acetate. Our experiments with sediments from soda lakes of Kulunda Steppe (Altai, Russia) showed sulfide production with sulfate as electron acceptor and propionate and butyrate (but not acetate) as an electron donor at a pH 10–10.5 and a salinity 70–180 g l?1. With propionate as substrate, a highly enriched sulfidogenic culture was obtained in which the main component was identified as a novel representative of the family Syntrophobacteraceae. With butyrate as substrate, a pure SRB culture was isolated which oxidized butyrate and some higher fatty acids incompletely to acetate. The strain represents the first haloalkaliphilic representative of the family Desulfobacteraceae and is described as Desulfobotulus alkaliphilus sp. nov. 相似文献