全文获取类型
收费全文 | 1766篇 |
免费 | 140篇 |
国内免费 | 2篇 |
专业分类
1908篇 |
出版年
2023年 | 37篇 |
2022年 | 17篇 |
2021年 | 30篇 |
2020年 | 30篇 |
2019年 | 37篇 |
2018年 | 60篇 |
2017年 | 54篇 |
2016年 | 99篇 |
2015年 | 80篇 |
2014年 | 102篇 |
2013年 | 233篇 |
2012年 | 108篇 |
2011年 | 143篇 |
2010年 | 158篇 |
2009年 | 98篇 |
2008年 | 69篇 |
2007年 | 29篇 |
2006年 | 42篇 |
2005年 | 25篇 |
2004年 | 32篇 |
2003年 | 18篇 |
2002年 | 18篇 |
2001年 | 18篇 |
2000年 | 12篇 |
1999年 | 11篇 |
1998年 | 16篇 |
1997年 | 10篇 |
1996年 | 19篇 |
1995年 | 15篇 |
1994年 | 14篇 |
1993年 | 25篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 11篇 |
1989年 | 5篇 |
1988年 | 14篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1972年 | 12篇 |
1971年 | 16篇 |
排序方式: 共有1908条查询结果,搜索用时 8 毫秒
61.
Ferenc Ötvös Dmitry S. Gembitsky Richard F. Murphy Sándor Lovas 《International journal of peptide research and therapeutics》2007,13(1-2):329-336
Steric requirements of binding [Nle10]NKA(4–10) to NK-2 receptor were studied by introducing conformationally constrained amino acid analogs into its sequence.
Two series of [Nle10]NKA(4–10) analogs were synthesized to investigate (i) the significance of a putative β-turn in the receptor-ligand interaction by insertion of either (S)- or (R)-Gly8{ANC-2}Leu9 γ-lactams to mimic a β-turn constraint, and (ii) the effect of hindered rotation in the Φ, χ1 and χ2 dihedral angle space of the crucially important Phe6 which was replaced systematically with d-Phe, d- and l-Tyr, as well as with their conformationally constrained analogs, Tic, HOTic and β-MePhe. Competition binding experiments
with [3H]NKA were performed using cloned human NK-2 receptors expressed in CHO cells. The analog possessing only an (R)-Gly8{ANC-2}Leu9 constraint, had the same binding affinity as that of the parent peptide. The rank order of potency of the other analogs showed
a cumulative effect of different structural modifications in decreasing the binding affinity, i.e., when changing the configuration of the lactam ring to S, replacing Phe6 with constrained analogs, Tic or β-MePhe, changing the configuration of the amino acid at position six to d, and introducing a hydroxyl group on the aromatic ring.
Ferenc ?tv?s and Dmitry S. Gembitsky - Made an equal contribution.
Abbreviations used for amino acids and peptides follow the recommendations of the IUPAC-IUB Commission of Biochemical Nomenclature,
Eur. J. Biochem. (1984) 138, 9–37 相似文献
62.
The soil fungi in the pure stand of oak (Quercus petraea), beech (Fagus orientalis), and pine (Pinus nigra) were investigated by the dilution plate method at Yildiz Mountain in Thrace region. The mycobiota, as well as the number of isolates per plate, was determined at various soil depths. Principal component analysis of the soil profiles indicated that there was variation in mycobiota composition and the variation was attributed to differences among the ecosystems. When comparing conifer and hardwood soils, using Sorenson’s similarity index, fungal community composition corresponded more closely between the hardwood stands than with the conifer stand. Fungal community composition appears to be influenced by the organic compounds entering soil from plant litter. 相似文献
63.
Özmen Serdar Demirci Tunhan Baydar Nilgün Göktürk 《In vitro cellular & developmental biology. Plant》2022,58(5):826-836
In Vitro Cellular & Developmental Biology - Plant - This study was carried out to determine the effects of 24-epibrassinolide (24-eBL) and methyl jasmonate (MeJA) on cell growth and... 相似文献
64.
Biology Bulletin - This study investigated the protective effects of quercetin (QUE) in doxorubicin (DOX)-induced testicular toxicity in rats. In the present study, testicular histomorphometry, the... 相似文献
65.
Extracellular proteases produced by Scytalidium thermophilum, grown on microcrystalline cellulose, were most active at pH 6.5–8 and 37–45 °C when incubated for 60 min. Highest protease activity was at day 3 where endoglucanase activity was low. Protease activity measurements with and without the protease inhibitors, p-chloromercuribenzoate, PMSF, antipain, E-64, EDTA and pepstatin A, suggest production of thiol-containing serine protease and serine proteases. Endoglucanase and Avicel-adsorbable endoglucanase activity in culture medium was not significantly affected by protease inhibitors. 相似文献
66.
SIRPA KAUNISTO PANU VÄLIMÄKI RAINE KORTET JANI KOSKIMÄKI SAULI HÄRKÖNEN ARJA KAITALA SAULI LAAKSONEN LAURA HÄRKÖNEN HANNU YLÖNEN 《Biological journal of the Linnean Society. Linnean Society of London》2012,106(2):275-286
The deer ked (Lipoptena cervi) is an ectoparasitic fly on cervids that has expanded its distribution rapidly in Northern Europe. However, the regulating biotic factors such as predation remain unknown. The host‐independent pupal stage of the fly lasts for several months. Blackish pupae are visible against snow, especially on the bedding sites of hosts, and are thus exposed to predators. To evaluate the role of predation on the invasion dynamics and evolution of L. cervi, we monitored pupal predation on artificial bedding sites in three geographical areas in Finland during winter. We explored: (1) possible predators; (2) magnitude of predation; and (3) whether predation risk is affected by host‐derived cues. We demonstrate that pupae are predated by a number of tit species. Any reddish brown snow discoloration on bedding sites, indicating heavy infestation of the host, serves as an exploitable cue for avian predators, thereby increasing the risk of pupal predation. The ability of tits to use this host‐derived cue seems to be dependent on the prevalence of L. cervi and the period of invasion history, which suggests that it may be a learned behavioural response. Predation by tits may potentially affect the L. cervi population dynamics locally. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 275–286. 相似文献
67.
Litman GW; Rast JP; Shamblott MJ; Haire RN; Hulst M; Roess W; Litman RT; Hinds- Frey KR; Zilch A; Amemiya CT 《Molecular biology and evolution》1993,10(1):60-72
Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
相似文献
68.
Ögren E 《Physiologia plantarum》2001,112(1):71-77
Effects of climatic warming on cold hardiness were investigated for some northern woody plants. In the first experiment, seedlings of Norway spruce ( Picea abies [L.] Karst.), Scots pine ( Pinus sylvestris L.) and lodgepole pine ( Pinus contorta Dougl. var. latifolia Engelm.) were exposed to naturally fluctuating temperatures averaging −6°C (ambient) and 0°C (elevated) for 16 weeks in midwinter before they were thawed and re-saturated with water. In lodgepole pine, needle sugar concentrations had decreased by 15%, and the temperature needed to induce 10% injury to needles in terms of electrolyte leakage had increased by 6°C following treatment to elevated as compared with control temperatures. In contrast, Norway spruce and Scots pine showed no effects. The lack of an effect for Scots pine was ascribed to seedlings containing unusually large energy reserves that buffered respiratory expenditure of sugars. A strong, linear relationship between levels of cold hardiness, assessed by the electrolyte leakage method, and sugars was found when combining data from this and previous, similar experiments. In the second experiment, the evergreen dwarf shrub Empetrum hermaphroditum Hagerup was analysed for leaf cold hardiness, using the electrolyte leakage method, and sugar concentrations in late spring and late autumn during the third year of a warming experiment in a subarctic dwarf shrub community. The objective was to test the hypothesis that warming in the growing season alters hardening/dehardening cycles by increasing soil nitrogen mineralization and plant growth. Data found, however, suggested that cold hardening/dehardening cycles were unaffected by warming. 相似文献
69.
Nitrogen and Phosphorus Limitation of Phytoplankton Growth in New Zealand Lakes: Implications for Eutrophication Control 总被引:6,自引:0,他引:6
We examine macronutrient limitation in New Zealand (NZ) lakes where, contrary to the phosphorus (P) only control paradigm,
nitrogen (N) control is widely adopted to alleviate eutrophication. A review of published results of nutrient enrichment experiments
showed that N more frequently limited lake productivity than P; however, stoichiometric analysis of a sample of 121 NZ lakes
indicates that the majority (52.9%) of lakes have a mean ratio of total nitrogen (TN) to total phosphorus (TP) (by mass) indicative
of potential P-limitation (>15:1), whereas only 14.0% of lakes have mean TN:TP indicative of potential N-limitation (<7:1).
Comparison of TN, TP, and chlorophyll a data between 121 NZ lakes and 689 lakes in 15 European Union (EU) countries suggests that at the national scale, N has a
greater role in determining lake productivity in NZ than in the EU. TN:TP is significantly lower in NZ lakes across all trophic
states, a difference that is driven primarily by significantly lower in-lake TN concentrations at low trophic states and significantly
higher TP concentrations at higher trophic states. The form of the TN:TP relationship differs between NZ and the EU countries,
suggesting that lake nutrient sources and/or loss mechanisms differ between the two regions. Dual control of N and P should
be the status quo for lacustrine eutrophication control in New Zealand and more effort is needed to reduce P inputs. 相似文献
70.
In this study, the relative growth, size–weight relationships and size at onset of maturity of the brown crab Cancer pagurus were investigated in the Isle of Man. For the analyses of relative growth and size at onset of maturity, the samples were collected seasonally between autumn 2012 and spring 2013 using several methods: pot surveys, dredge and trawl surveys, market surveys and shore surveys. Results showed that allometric growth occurred in the chelipeds of males (n?=?87) and in the abdomen of females (n?=?222). Four different measures of maturity (behavioural, functional, morphometric and physiological) were examined. With respect to the behavioural maturity, the smallest female crab found with a sperm plug measured 110?mm CW, whereas in terms of functional maturity the smallest ovigerous female had a CW of 134?mm. Based on direct observations of gonad maturity, 50% of females were mature at 108?mm CW, whereas 50% of males were mature at 89?mm CW. The size at the onset of maturity measurements of female and male C. pagurus based on gonad development is smaller than the current minimum landing size (130?mm), and therefore this suggests that the current minimum landing size is an adequate management measure. 相似文献