全文获取类型
收费全文 | 1150篇 |
免费 | 100篇 |
出版年
2022年 | 7篇 |
2021年 | 13篇 |
2020年 | 9篇 |
2019年 | 13篇 |
2018年 | 22篇 |
2017年 | 10篇 |
2016年 | 20篇 |
2015年 | 48篇 |
2014年 | 51篇 |
2013年 | 56篇 |
2012年 | 78篇 |
2011年 | 64篇 |
2010年 | 35篇 |
2009年 | 34篇 |
2008年 | 61篇 |
2007年 | 67篇 |
2006年 | 38篇 |
2005年 | 45篇 |
2004年 | 38篇 |
2003年 | 56篇 |
2002年 | 50篇 |
2001年 | 42篇 |
2000年 | 32篇 |
1999年 | 24篇 |
1998年 | 22篇 |
1997年 | 16篇 |
1996年 | 8篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 18篇 |
1992年 | 25篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 17篇 |
1987年 | 14篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1976年 | 5篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1972年 | 6篇 |
1970年 | 6篇 |
1968年 | 8篇 |
排序方式: 共有1250条查询结果,搜索用时 15 毫秒
1.
K M Le B L Madsen P W Barth G A Ksander J B Angell L M Vistnes 《Plastic and reconstructive surgery》1984,74(6):745-756
Three-dimensional scalar pressure distributions were measured in solid tissue near bony prominences in vitro in meat and in vivo in pigs using silicon pressure sensors. Data are in accord with previous theoretical models and indicate that pressure is three to five times higher internally near a bony prominence than it is at the skin over the prominence. Pressure sores are thus thought to begin internally; by the time they are evident at the skin, the sore has worked its way completely from bone to skin. This conclusion is in accord with previous clinical data. Future measurement of local vector forces is needed to fully characterize the force distribution in vivo. 相似文献
2.
Statistical inference from single channel records: two-state Markov model with limited time resolution 总被引:4,自引:0,他引:4
G F Yeo R K Milne R O Edeson B W Madsen 《Proceedings of the Royal Society of London. Series B, Containing papers of a Biological character. Royal Society (Great Britain)》1988,235(1278):63-94
Though stochastic models are widely used to describe single ion channel behaviour, statistical inference based on them has received little consideration. This paper describes techniques of statistical inference, in particular likelihood methods, suitable for Markov models incorporating limited time resolution by means of a discrete detection limit. To simplify the analysis, attention is restricted to two-state models, although the methods have more general applicability. Non-uniqueness of the mean open-time and mean closed-time estimators obtained by moment methods based on single exponential approximations to the apparent open-time and apparent closed-time distributions has been reported. The present study clarifies and extends this previous work by proving that, for such approximations, the likelihood equations as well as the moment equations (usually) have multiple solutions. Such non-uniqueness corresponds to non-identifiability of the statistical model for the apparent quantities. By contrast, higher-order approximations yield theoretically identifiable models. Likelihood-based estimation procedures are developed for both single exponential and bi-exponential approximations. The methods and results are illustrated by numerical examples based on literature and simulated data, with consideration given to empirical distributions and model control, likelihood plots, and point estimation and confidence regions. 相似文献
3.
Data from 814 cows involved in five separate full lactation studies were used to assess the effect of recombinantly-derived methionyl bovine somatotropin (sometribove) on reproductive performance. Data were separated by parity (first and second or greater), route of administration (intramuscular: i.m. or subcutaneous: s.c.), length of breeding period (number of days in milk), and level of production (high vs low). Through 305 days in milk, pregnancy rates were reduced 18% in primiparous, sometribove-treated (i.m.) cows but were not significantly affected in multiparous cows. No differences were noted in either parity group when sometribove was administered subcutaneously. The level of production was more often found to be a significant factor affecting reproductive parameters than was sometribove administration. In general, length of the breeding period and level of milk production had a greater influence on reproductive performance than treatment with sometribove. 相似文献
4.
Cloning and characterization of two plasmids from Bacillus thuringiensis in Bacillus subtilis 总被引:8,自引:0,他引:8
Bacillus thuringiensis subspecies israliensis plasmids pTX14-1 and pTX14-3 were cloned and analyzed by Southern blot hybridization for their replication mechanism in Bacillus subtilis. The cloning of pTX14-1 into the replicon deficient vector pBOE335 showed the usual characteristics of single-stranded DNA plasmids, i.e., it generated circular single-stranded DNA and high molecular weight (HMW) multimers. The other plasmid, pTX14-3, behaved differently; it generated neither single-stranded DNA nor HMW multimers. Treatment with rifampicin did not result in the accumulation of single-stranded DNA. However, deletion of an EcoRI-PstI fragment resulted in the accumulation of both single-stranded DNA and HMW multimers. From various deletion derivatives, we have mapped the minus origin and the locus responsible for suppression of HMW multimer formation. Full activity of the minus origin and of the locus suppressing HMW formation was only observed on the native replicon, indicating a coupling to the plus strand synthesis. 相似文献
5.
A Celis P Madsen H V Nielsen H H Rasmussen H Thiessen J B Lauridsen B van Deurs J E Celis 《FEBS letters》1988,227(1):14-20
A mouse monoclonal antibody (mAB 22-II-D8B) raised against lysed transformed human amnion cells (AMA) has been characterized. The mAB decorated the Golgi apparatus in growing and quiescent cultured monolayer cells (fibroblasts and epithelial cells) of various species as determined by double immunofluorescence labeling and colocalization with galactosyltransferase antibodies. It reacted with the acidic human proteins IEF 58 (Mr = 29,000) and 57a, respectively (Mr = 30,000) (HeLa protein catalogue number; [(1982) Clin. Chem. 28, 766]), Golgi staining was also observed in BS-C-1 cells microinjected with mAB 22-II-D8B suggesting that the epitopes recognized by the antibody are most likely located on the cytoplasmic face of the membranes. The precise localization of the antigens to the various cisternae of the Golgi apparatus could not be demonstrated by immunogold cytochemistry on ultrathin cryosections due to either weak reactivity of the antibody or low concentration of the antigens. Immunofluorescence staining with mAB 22-II-D8B of lymphoid human Molt-4 cells and some human tissues failed to reveal any significant staining even though these expressed high levels of both IEF 58 and 57a. These results are taken to imply that the epitopes recognized by mAB 22-II-D8B may be masked in some cell types. 相似文献
6.
7.
The binding of glucose and a series of oligosaccharides to glycogen debranching enzyme was determined by the ability of the saccharides to decrease the rate of reaction of sulfhydryl groups with 5,5'-dithiobis(2-nitrobenzoate) (DTNB). At pH 7.2, the strength of binding increases with chain length from glucose to maltotriose to maltopentaose but not to maltohexaose, and the free energies for binding of the oligosaccharides suggest subsites of equivalent affinities for the four glucose units following the initial reducing moiety. The rate of reaction of DTNB with enzyme saturated with saccharide is the same for all compounds, suggesting that all the saccharides, including glucose, induce the same conformational state. The site of binding may be that which binds the alpha-1,6-linked side chain of the natural limit dextrin substrate. At pH 8.0, this site exhibits similar characteristics, but an additional site, which may bind the four terminal glucose units of the main chain of the natural substrate, is manifested and exhibits different characteristics, including a very low affinity for glucose itself. The binding of glycogen to the debranching enzyme was monitored by centrifugal separation from the protein and exhibits a much lower dissociation constant than that for the oligomers, suggesting that branched polymers have more than one set of subsites. 相似文献
8.
Constrained conformational energy minimizations have been used to calculate an adiabatic (Φ, ψ) potential energy surface for the disaccharide β-maltose. The inclusion of molecular flexibility in the conformational energy analysis of the disaccharide was found to significantly lower the barriers to conformational transitions, as has been observed previously for other systems. Several low energy wells were identified on the adiabatic surface which differ in energy by small amounts and with low absolute barriers separating them, indicating the possibility of a non-negligible equilibrium population distribution in each well. If such a distribution of conformations existed in the physical system, the conformation observed by NMR NOE measurements would thus be a “virtual” conformation. Molecular dynamics simulations of the motions of this molecule in vacuum were also conducted and indicate that the rate of relaxation of the molecule to the adiabatic surface may be slower than the typical timescale of conformational fluctuations. This effect is apparently due to an unphysical persistence of hydrogen bond patterns in vacuum which does not occur in aqueous solution. Trajectories undergoing transitions between wells were calculated and the effects of such conformational transitions upon the ensemble mean structure, such as might be observed in an NMR experiment, were demonstrated. 相似文献
9.
Immunoreactivity for laminin in the developing ventral longitudinal pathway of the brain 总被引:7,自引:0,他引:7
The first long tract to form in the brain of a vertebrate embryo is the ventral longitudinal pathway. In order to investigate what chemical cues may guide nerve growth cones along this pathway, affinity-purified antibodies to laminin and collagen type IV were used to stain sections of mouse embryos from Embryonic Days 8 through 17. A monoclonal anti-neurofilament antibody was used to show the development of the ventral longitudinal pathway in relationship to immunoreactivity for laminin and collagen type IV. At Day 8 fluorescent immunoreactivity for laminin is bright in the external limiting membrane of the neural tube, but the neuroepithelium does not show bright laminin or neurofilament immunoreactivity. At E9 the ventral longitudinal pathway is forming and punctate immunoreactivity for laminin is present on the surfaces of neuroepithelial cells in the marginal zone, through which axons of the ventral pathway extend. Punctate immunofluorescence for laminin remains concentrated in the marginal zone on Days E10 through E14, but on E16 punctate immunofluorescence was much reduced, although immunoreactivity for laminin remained bright in the maturing pial and arachnoid membranes and on blood vessels in the brain. Immunoreactivity for collagen type IV was strong in the external limiting membrane and on blood vessels, but never showed concentrated punctate immunofluorescence in the marginal zone. These results indicate that laminin may be available on cell surfaces and in extracellular spaces as an adhesive ligand for growth cones during the formation of the ventral longitudinal pathway. 相似文献
10.
Association of the M blood group system with bovine mastitis 总被引:2,自引:0,他引:2
B Larsen N E Jensen P Madsen S M Nielsen O Klastrup P S Madsen 《Animal blood groups and biochemical genetics》1985,16(3):165-173
Associations of the 11 bovine blood group systems with mastitis were examined in Red Danish dairy cattle. The mastitis status was followed during three lactational periods. A significant effect of the M blood group system on mastitis incidence was observed in the first and second lactation periods and a lower frequency of mastitis is found among animals lacking the M' factor as compared to those having the M' blood group factor. The significance of these results are discussed in view of the close relation between the M blood group system and the bovine lymphocyte antigens (BoLA), and the expected effect of eliminating the M' gene from the breed is estimated. Among the remaining 10 blood group systems, the T' system was the only system showing an overall effect on mastitis, and only in first and third lactation. However, the T' system was inconsistent with regard to the effect of the T' gene on the various mastitis diagnoses. 相似文献