全文获取类型
收费全文 | 15577篇 |
免费 | 1572篇 |
国内免费 | 19篇 |
出版年
2023年 | 75篇 |
2022年 | 86篇 |
2021年 | 373篇 |
2020年 | 180篇 |
2019年 | 275篇 |
2018年 | 310篇 |
2017年 | 291篇 |
2016年 | 443篇 |
2015年 | 780篇 |
2014年 | 808篇 |
2013年 | 997篇 |
2012年 | 1198篇 |
2011年 | 1168篇 |
2010年 | 720篇 |
2009年 | 644篇 |
2008年 | 840篇 |
2007年 | 896篇 |
2006年 | 762篇 |
2005年 | 720篇 |
2004年 | 709篇 |
2003年 | 589篇 |
2002年 | 586篇 |
2001年 | 244篇 |
2000年 | 248篇 |
1999年 | 213篇 |
1998年 | 180篇 |
1997年 | 138篇 |
1996年 | 143篇 |
1995年 | 137篇 |
1994年 | 111篇 |
1993年 | 128篇 |
1992年 | 151篇 |
1991年 | 126篇 |
1990年 | 119篇 |
1989年 | 119篇 |
1988年 | 112篇 |
1987年 | 92篇 |
1986年 | 94篇 |
1985年 | 121篇 |
1984年 | 97篇 |
1983年 | 80篇 |
1982年 | 84篇 |
1981年 | 63篇 |
1980年 | 60篇 |
1979年 | 69篇 |
1978年 | 61篇 |
1977年 | 68篇 |
1976年 | 63篇 |
1974年 | 62篇 |
1973年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
L Nagy G Nagy I Rácz L Simon I Solt I Patty F Tárnok G Mózsik T Jávor 《Acta physiologica Hungarica》1989,73(2-3):331-339
TISACID (a new, modern Hungarian Al-containing antacid) with a high acid-neutralizing capacity (greater than 26.8 mmol/g) also enhances gastric mucosal defense mechanisms (prostaglandin-dependent gastroprotection). A simple-blind, prospective, randomized, parallel multicentre clinical trial has been performed on both the clinical efficacy and possible side effects of TISACID monotherapy (Al-Mg-hydroxy-carbonate) on informed patients suffering from active duodenal ulcers. The study groups were as follows: Group "A": 3 g/day of TISACID (acid-neutralizing capacity = 78 mmol, n = 85), Group "B": 6 g/day of TISACID (acid-neutralizing capacity = 156 mmol, n = 88), Group "C": 12 g/day of TISACID (acid-neutralizing capacity = 312 mmol, n = 68), Group "D": (as control): (1.0 g/day cimetidine (HISTODIL, RGH, Budapest, n = 91). The total number of patients: 332. It was found that: 1. The new Hungarian antacid compound (both tablet and suspension) can essentially accelerate the healing rate of duodenal ulcers. 2. The cumulative healing rate of ulcers and the decrease of complaints can be achieved equally by relatively low doses of TISACID monotherapy and cimetidine alone. 3. There were no differences between the clinical potency and side-effects of TISACID tablet and suspension. 相似文献
62.
Differential gene expression during mouse spermatogenesis 总被引:9,自引:0,他引:9
K H Thomas T M Wilkie P Tomashefsky A R Bellvé M I Simon 《Biology of reproduction》1989,41(4):729-739
63.
Carboxylic acid reductase: a new tungsten enzyme catalyses the reduction of non-activated carboxylic acids to aldehydes 总被引:8,自引:0,他引:8
An enzyme which we call carboxylic acid reductase (aldehyde dehydrogenase) seems to be the first which is able to reduce non-activated carboxylic acids to aldehydes at the expense of reduced viologens. There is no further reduction of the aldehydes to the corresponding alcohols. In the presence of oxidized viologens aldehydes can be dehydrogenated to carboxylic acids roughly 20 times faster than the latter are reduced. The specific enzyme activity in crude extracts is about 100 times increased if 10 microM tungstate and a sulphur source in addition to sulphate is given to the growth medium of Clostridium thermoaceticum. Carboxylic acid reductase seems to be present in two forms. One has an apparent molecular mass of about 240 kDa and is bound to red-Sepharose, whereas, the other, a form of an apparent molecular mass of about 60 kDa, is not bound. SDS gel electrophoresis shows a higher complexity. The very labile enzyme has been enriched by a factor of about 145 by binding to octyl-Sepharose and further chromatographic separation by red-Sepharose and FPLC using Mono-Q and phenyl-Superose columns. After cell growth in the presence of [185W]tungstate, radioactivity coincides with the two forms of enzyme activity during all purification steps. This is also the case when the enzyme is electrophoretically separated on polyacrylamide slab gels. 相似文献
64.
K Hubrich-Kühner H J Buhk H Wagner H Kr?ger D Simon 《Biochemical and biophysical research communications》1989,160(3):1175-1182
The eukaryotic DNA cytosine-5-methyltransferase (E.C.2.1.1.37) is known to methylate cytosine in DNA mainly, but not exclusively in C-G. In the present study the minor, non-C-G recognition sequences of a rat DNA methyltransferase were analyzed by Maxam-Gilbert sequencing of in vitro methylated SV40 DNA. The enzyme methylates C-A and C-T at a 50-fold lower initial rate than C-G. Methylation of C-C at the 5'C was not observed in the piece of DNA sequenced. The methylation of C-A is very low in the trinucleotides ACA and CAC, the other C-A containing trinucleotides in DNA are much better methylacceptors. C-T was found methylated predominantly in the sequences CCTAA, ACTAA, and ACTGT. A comparison of the activity with different substrates is in favour of the enzyme making its recognition in the major groove of the DNA. 相似文献
65.
Liang Zhong Chen Simon Easteal Philip G. Board Kim M. Summers Kuldeep K. Bhatia Robert L. Kirk 《Human genetics》1990,85(1):89-97
Summary We have determined the various haplotypic combinations between alleles as well as restriction fragment length polymorphisms of two linked genetic markers, albumin and vitamin D-binding protein or group-specific component, in a number of Asian-Pacific populations. Using the partial maximum likelihood method, we constructed a phylogenetic network from the haplotype frequencies to assess relationships among the populations sampled. No systematic linkage disequilibrium was detected between most of the combinations, suggesting a lack of operation of any selection pressure at the two loci. The phylogenetic analysis confirmed the known interrelationships among various populations in the Asian-Pacific region. The Australian aborigines clustered closely with the non-Austronesian-speaking highlanders from Papua New Guinea, as expected. Similarly, the Austronesian-speaking Polynesians, Micronesians, and the Southeast Asians branched off together as a separate group. The position of the Austronesian-speaking Tolais from New Britain with respect to other populations from the Southwest Pacific was anomalous. The Tolais revealed a strong affinity with the Australian aborigines, which is inexplicable. The populations from China formed a tight cluster with other populations from the Asian-Pacific region. Genetic interrelationships of these populations with the white Australians were remote, which is in accordance with the known affinities of various human racial groups. 相似文献
66.
Ted W. Simon Donald H. Edwards 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1990,166(6):745-755
The caudal photoreceptors (CPRs) of crayfish (Procambarus clarkii) can trigger walking and abdominal movements by their response to light.
相似文献
1. | In a restrained, inverted crayfish, illumination of A6 evoked a CPR discharge followed by leg movements and bursting from the abdominal tonic flexor (TF) motoneurons. Intracellular electrical stimulation of a single CPR at high frequency (80 Hz) evoked similar responses. |
2. | Responses only occurred when a single CPR axon was driven at 60 Hz or more and outlasted the stimulus. |
3. | CPR stimulation also excites the pattern-initiating network (Moore and Larimer 1987) in the abdomen. |
4. | The axon of the CPR projects from ganglion A6 to the brain. Terminal branches occur in the subesophageal ganglion and the brain. A small descending interneuron is dye-coupled to CPR in the subesophageal ganglion. |
5. | In animals with cut circumesophageal connectives, the CPRs can evoke walking and the abdominal motor pattern. |
6. | The relationship of the abdominal motor pattern to walking is altered by restraint and/or inversion. In freely moving crayfish, the cyclic abdominal motor pattern is only observed with backward walking. In restrained, inverted crayfish, the motor pattern occurs with both forward or backward walking. |
67.
Developmental regulation of expression of the lactate dehydrogenase (LDH) multigene family during mouse spermatogenesis 总被引:4,自引:0,他引:4
K Thomas J Del Mazo P Eversole A Bellvé Y Hiraoka S S Li M Simon 《Development (Cambridge, England)》1990,109(2):483-493
Expression of the Lactate Dehydrogenase (LDH) genes during various stages of spermatogenesis was studied by using a combination of Northern blot analyses and in situ hybridization techniques. These studies have indicated that developmentally programmed expression of all three functional LDH genes occurs during differentiation of germ cells. The LDH/C (ldh-3) gene was expressed exclusively during meiosis and spermiogenesis, beginning in leptotene/zygotene spermatocytes and continuing through to the elongated spermatids. LDH/C (ldh-3) gene expression was accompanied by transient expression of the LDH/A (ldh-1) gene in pachytene spermatocytes and round spermatids. The LDH/B (ldh-2) gene was expressed mainly in Sertoli and spermatogonial cells. By using somatic cell hybrids, the LDH/C (ldh-3) gene has been mapped to mouse chromosome 7, establishing that it is syntenic with the LDH/A (ldh-1) gene locus. Experimental observations made in this study provide new insight into the order and sequence of events involved in the regulation of gene expression of the LDH gene family during spermatogenesis. 相似文献
68.
69.
We isolated and characterized two related ubiquitin genes from Drosophila melanogaster, polyubiquitin and UB3-D. The polyubiquitin gene contained 18 repeats of the 228-base-pair monomeric ubiquitin-encoding unit arranged in tandem. This gene was localized to a minor heat shock puff site, 63F, and it encoded a constitutively expressed 4.4-kilobase polyubiquitin-encoding mRNA, whose level was induced threefold by heat shock. To investigate the pattern of expression of the polyubiquitin gene in developing animals, a polyubiquitin-lacZ fusion gene was introduced into the Drosophila genome by germ line transformation. The fusion gene was expressed at high levels in a tissue-general manner at all life stages assayed. The ubiquitin-encoding gene, UB3-D, consisted of one ubiquitin-encoding unit directly fused, in frame, to a nonhomologous tail sequence. The amino acid sequence of the tail portion of the protein had 65% positional identity with that of yeast UBI3 protein, including a region that contained a potential nucleic acid-binding motif. The Drosophila UB3-D gene hybridized to a 0.9-kilobase mRNA that was constitutively expressed, and in contrast to the polyubiquitin gene, it was not inducible by heat shock. 相似文献
70.
Summary By use of antisera raised against purified moultinhibiting (MIH) and crustacean hyperglycemic hormone (CHH) from Carcinus maenas, complete and distinct neurosecretory pathways for both hormones were demonstrated with the PAP and immunofluorescence technique. By double staining, employing a combination of silver-enhanced immunogold labelling and PAP, both antigens could be visualized in the same section. Immunoreactive structures were studied in Carcinus maenas, Liocarcinus puber, Cancer pagurus, Uca pugilator and Maja squinado. They were only observed in the X-organ sinus gland (SG) system of the eyestalks and consisted of MIH-positive perikarya, which were dispersed among the more numerous CHH-positive perikarya of the medulla terminalis X-organ (XO). The MIH-positive neurons form branching collateral plexuses adjacent to the XO and axons that are arranged around the CHH-positive central axon bundle of the principal XO-SG tract. In the SG, MIH-positive axon profiles and terminals, clustered around hemolymph lacunae, are distributed between the more abundant CHH-positive axon profiles and terminals. Colocalisation of MIH and CHH was never observed. The gross morphology of both neurosecretory systems was similar in all species examined, however, in U. pugilator and M. squinado immunostaining for MIH was relatively faint unless higher concentrations of antiserum were used. Possible reasons for this phenomenon as well as observed moult cycle-related differences in immunostaining are discussed. 相似文献