全文获取类型
收费全文 | 13920篇 |
免费 | 427篇 |
国内免费 | 902篇 |
出版年
2023年 | 107篇 |
2022年 | 189篇 |
2021年 | 248篇 |
2020年 | 178篇 |
2019年 | 204篇 |
2018年 | 181篇 |
2017年 | 166篇 |
2016年 | 227篇 |
2015年 | 266篇 |
2014年 | 613篇 |
2013年 | 828篇 |
2012年 | 638篇 |
2011年 | 618篇 |
2010年 | 490篇 |
2009年 | 575篇 |
2008年 | 663篇 |
2007年 | 693篇 |
2006年 | 640篇 |
2005年 | 671篇 |
2004年 | 598篇 |
2003年 | 541篇 |
2002年 | 484篇 |
2001年 | 330篇 |
2000年 | 293篇 |
1999年 | 343篇 |
1998年 | 284篇 |
1997年 | 310篇 |
1996年 | 281篇 |
1995年 | 297篇 |
1994年 | 287篇 |
1993年 | 290篇 |
1992年 | 255篇 |
1991年 | 212篇 |
1990年 | 186篇 |
1989年 | 182篇 |
1988年 | 170篇 |
1987年 | 171篇 |
1986年 | 129篇 |
1985年 | 217篇 |
1984年 | 187篇 |
1983年 | 136篇 |
1982年 | 184篇 |
1981年 | 142篇 |
1980年 | 123篇 |
1979年 | 117篇 |
1978年 | 60篇 |
1977年 | 65篇 |
1976年 | 54篇 |
1974年 | 26篇 |
1973年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Abalone are semimobile marine gastropods that form the basis of Australia's second most valuable fishery. A site off the coast of Port Arthur, Tasmania, was visited on six occasions. On each occasion, any unmarked live abalone found were marked with a unique identification number and were recorded. Any previously marked abalone found had its identification number and whether or not it was still alive recorded. This results in integrated mark-recapture-recovery data, as in Catchpole et al. (1998, Biometrics 54, 33-46). During the study period, abalone grew in size, and we model the survival of individuals as a function of their size, estimated from a fitted growth curve. The shells of dead animals are long lasting, and we extend existing methodology to allow for the possibility that an animal found dead may have been dead but overlooked for several visits. 相似文献
32.
J. M. Diez G. Giannicot † E. McLeant † E. M. Donaldson †‡ 《Journal of fish biology》1992,40(6):887-893
Porcine galanin, somatostatins (SRIF-25 and SRIF-28) and invariant SRIF-14, known to have inhibitory-stimulatory actions on growth hormone (GH) secretion in higher vertebrates, were tested for their ability to affect plasma GH levels in coho salmon. Peptides were administered by intraperitoneal injection of 10 or 100 ng g−1 body weight. All three SRIFs decreased plasma GH concentrations, their activity following the order SRIF-14 > SRIF-28 > SRIF-25. Galanin and an anti-SRIF produced pronounced, although transient increases in plasma GH. 相似文献
33.
Native bovine parathyroid hormone (bPTH) was found to be readily cleaved with human leukocyte elastase to yield the fragments bPTH(1–41) and bPTH(42–84). These were then isolated by reverse-phase HPLC and characterised by gas-phase sequencing and amino acid analysis. The biological activities of these fragments were assessed in an adenylate cyclase bioassay using the rat osteosarcoma cell line UMR106. bPTH(1–41) was found to have approximately twice the molar potency of the native hormone from which it was derived, bPTH(42–84) had no biological activity and did not modulate the adenylate cyclase response to these cells to the native hormone. The possible physiological significance of these observations is discussed. 相似文献
34.
Two full-length (or nearly so) cDNA clones containing information for the protease inhibitors PI IV and C-II from soybean seeds were identified by means of a synthetic probe. DNA sequencing revealed that the two protease inhibitors are synthesized as precursors with a short peptide leader. The coding regions of the two clones show 80% homology, wheraes the 5 non-coding regions are 90% homologous. Homology of 75% is found in the region extending beyond the stop codons. 相似文献
35.
Four new auxin-responsive RNAs from soybean (Glycine max (L.) Merr., var. Wayne) are described. The RNAs were identified by hybridization to three cDNA probes obtained from a library enriched for sequences which increase in abundance within 60 min after 2,4-D (2,4-dichlorophenoxyacetic acid) treatment. These RNAs appear to define a new class of small (i.e. approximately 550 nucleotides) RNAs that respond extremely rapidly to application of exogenous auxin. In excised elongating hypocotyl sections, an increase in the abundance of these RNAs can be detected 2 to 5 min after treatment with 50 M 2,4-D. This response is half maximal after 10 min and reaches steady state in 60 min. RNA blot analysis shows that these RNAs are expressed differentially in various parts of the seedling. The degree of inducibility by auxin is also organ-specific, with the elongating hypocotyl being the most responsive of the organs tested. The RNAs display identical response specificities with one exception. Accumulation of one RNA, designated 10A, is completely abolished by simultaneous addition of cycloheximide and 2,4-D. This RNA also displays a different 2,4-D dose response than other RNAs examined. These results suggest that more than one mechanism is involved in rapid modulation of gene expression by auxin. 相似文献
36.
Amino Acid Sequences of Neuropeptides in the Sinus Gland of the Land Crab Cardisoma carnifex: A Novel Neuropeptide Proteolysis Site 总被引:1,自引:0,他引:1
Robert W. Newcomb 《Journal of neurochemistry》1987,49(2):574-583
The sinus gland is a major neurosecretory structure in Crustacea. Five peptides, labeled C, D, E, F, and I, isolated from the sinus gland of the land crab have been hypothesized to arise from the incomplete proteolysis at two internal sites on a single biosynthetic intermediate peptide "H", based on amino acid composition additivities and pulse-chase radiolabeling studies. The presence of only a single major precursor for the sinus gland peptides implies that peptide H may be synthesized on a common precursor with crustacean hyperglycemic hormone forms, "J" and "L," and a peptide, "K," similar to peptides with molt inhibiting activity. Here I report amino acid sequences of these peptides. The amino terminal sequence of the parent peptide, H, (and the homologous fragments) proved refractory to Edman degradation. Data from amino acid analysis and carboxypeptidase digestion of the naturally occurring fragments and of fragments produced by endopeptidase digestion were used together with Edman degradation to obtain the sequences. Amino acid analysis of fragments of the naturally occurring "overlap" peptides (those produced by internal cleavage at one site on H) was used to obtain the sequences across the cleavage sites. The amino acid sequence of the land crab peptide H is Arg-Ser-Ala-Asp-Gly-Phe-Gly-Arg-Met-Glu-Ser-Leu-Leu-Thr-Ser-Leu-Arg-Gly- Ser-Ala-Glu- Ser-Pro-Ala-Ala-Leu-Gly-Glu-Ala-Ser-Ala-Ala-His-Pro-Leu-Glu. In vivo cleavage at one site involves excision of arginine from the sequence Leu-Arg-Gly, whereas cleavage at the other site involves excision of serine from the sequence Glu-Ser-Leu. Proteolysis at the latter sequence has not been previously reported in intact secretory granules. The aspartate at position 4 is possibly covalently modified. 相似文献
37.
L. L. Wallace 《Oecologia》1987,72(3):423-428
Summary A factorial design of clipping and compaction was used to study the responses of Schizachyrium scoparium and its mycorrhizal symbionts to these stresses. All treatment combinations significantly reduced the growth and biomass of plants relative to controls. Compaction significantly reduced tillering and crown expansion while clipping increased tillering early in the growing season and reduced it later. Mycorrhizal colonization of roots was highest in the clipped plots and lowest in compacted plots. Spore number was highest in compacted plots and lowest in clipped plots. It appears that spore number may be negatively correlated with root growth since any treatment that reduced plant growth yielded higher spore numbers. The combination of clipping and compaction reduced plant growth the most, but had intermediate effects on mycorrhizal colonization and spore number. 相似文献
38.
The function of the epidermis in auxinmediated elongation growth of maize (Zea mays L.) coleoptile segments was investigated. The following results were obtained: i) In the intact organ, there is a strong tissue tension produced by the expanding force of the inner tissues which is balanced by the contracting force of the outer epidermal wall. The compression imposed by the stretched outer epidermal wall upon the inner tissues gives rise to a wall-pressure difference which can be transformed into a water-potential difference between inner tissues and external medium (water) by removal of the outer epidermal wall. ii) Peeled segments fail to respond to auxin with normal growth. The plastic extensibility of the inner-tissue cell walls (measured with a constant-load extensiometer using living segments) is not influenced by auxin (or abscisic acid) in peeled or nonpeeled segments. It is concluded that auxin induces (and abscisic acid inhibits) elongation of the intact segment by increasing (decreasing) the extensibility specifically in the outer epidermal wall. In addition, tissue tension (and therewith the pressure acting on the outer epidermal wall) is maintained at a constant level over several hours of auxin-mediated growth, indicating that the inner cells also contribute actively to organ elongation. However, this contribution does not involve an increase of cell-wall extensibility, but a continuous shifting of the potential extension threshold (i.e., the length to which the inner tissues would extend by water uptake after peeling) ahead of the actual segment length. Thus, steady growth involves the coordinated action of wall loosening in the epidermis and regeneration of tissue tension by the inner tissues. iii) Electron micrographs show the accumulation of striking osmiophilic material (particles of approx. 0.3 m diameter) specifically at the plasma membrane/cell-wall interface of the outer epidermal wall of auxin-treated segments. iv) Peeled segments fail to respond to auxin with proton excretion. This is in contrast to fusicoccin-induced proton excretion and growth which can also be readily demonstrated in the absence of the epidermis. However, peeled and nonpeeled segments show the same sensitivity to protons with regard to the induction of acid-mediated in-vivo elongation and cell-wall extensibility. The observed threshold at pH 4.5–5.0 is too low to be compatible with a second messenger function of protons also in the growth response of the inner tissues. Organ growth is described in terms of a physical model which takes into account tissue tension and extensibility of the outer epidermal wall as the decisive growth parameters. This model states that the wall pressure increment, produced by tissue tension in the outer epidermal wall, rather than the pressure acting on the inner-tissue walls, is the driving force of growth.Abbreviations and symbols
E
el, E
pl
elastic and plastic in-vitro cell-wall extensibility, respectively
-
E
tot
E
el+E
pl
- FC
fusicoccin
- IAA
indole-3-acetic acid
- IT
inner tissue
- ITW
inner-tissue walls
- OEW
outer epidermal wall
-
osmotic pressure
-
P
wall pressure
-
water potential 相似文献
39.
A. Tyagi J. Hermans J. Steppuhn Ch. Jansson F. Vater R. G. Herrmann 《Molecular & general genetics : MGG》1987,207(2-3):288-293
Summary Several cDNA clones encoding the 33 kDa protein associated with the photosynthetic water oxidation activity of spinach were sequenced. A 1208 bp insert of one of the clones encodes the entire 331 amino acid residues of the precursor protein including 84 amino acids (8.5 kDa) of the amino-terminal transit peptide, 49 bp of the 5 and 111 bp of the 3 untranslated segment of the mRNA. The 3 poly(A) tail starts 19 bp downstream from a putative polyadenylation signal, TATAAA. The hydrophilic mature protein consists of 247 amino acid residues corresponding to an Mr of 26.5 kDa, which is 6.5 kDa smaller than the value determined by SDS-polyacrylamide gel electrophoresis (33–34 kDa), and shows a certain degree of conservation with the putative Mn-complexing active sites of bacterial Mn-dependent superoxide dismutases. The anatomy of the unusually long transit sequence is discussed with regard to current concepts of protein import into and protein routein within the organelle. 相似文献
40.
S. R. Saif 《Plant and Soil》1987,97(1):25-35
Summary Growth and mineral uptake of twenty-four tropical forage legumes and grasses were compared under glasshouse conditions in a sterile low P oxisol, one part inoculated and the other not inoculated with mycorrhizal fungi. Shoot and root dry weights and total uptake of P, N, K, Ca, and Mg of all the test plants were significantly increased by mycorrhizal inoculation. Mycorrhizal inoculation, with few exceptions, decreased the root/shoot ratio. Non-mycorrhizal plants contained always lower quantities of mineral elements than mycorrhizal plants. Plant species showed differences in percentage mycorrhizal root length and there was no correlation between percentage mycorrhizal infection and plant growth parameters. A great variation in dependence on mycorrhiza was observed among forage species. Total uptake of all elements by non-mycorrhizal legumes and uptake of P, N and K by non-mycorrhizal grasses correlated inversely with mycorrhizal dependency. Mycorrhizal plants of all species used significantly greater quantities of soil P than the nonmycorrhizal plants. Utilization of soil P by non-mycorrhizal plants was correlated inversely with mycorrhizal dependency. 相似文献