全文获取类型
收费全文 | 2042篇 |
免费 | 195篇 |
出版年
2023年 | 16篇 |
2022年 | 17篇 |
2021年 | 39篇 |
2020年 | 36篇 |
2019年 | 28篇 |
2018年 | 27篇 |
2017年 | 33篇 |
2016年 | 53篇 |
2015年 | 86篇 |
2014年 | 93篇 |
2013年 | 103篇 |
2012年 | 126篇 |
2011年 | 89篇 |
2010年 | 53篇 |
2009年 | 65篇 |
2008年 | 82篇 |
2007年 | 94篇 |
2006年 | 105篇 |
2005年 | 75篇 |
2004年 | 90篇 |
2003年 | 74篇 |
2002年 | 74篇 |
2001年 | 52篇 |
2000年 | 58篇 |
1999年 | 51篇 |
1998年 | 20篇 |
1997年 | 15篇 |
1996年 | 26篇 |
1995年 | 28篇 |
1994年 | 18篇 |
1993年 | 28篇 |
1992年 | 35篇 |
1991年 | 42篇 |
1990年 | 39篇 |
1989年 | 29篇 |
1988年 | 20篇 |
1987年 | 25篇 |
1986年 | 27篇 |
1985年 | 35篇 |
1984年 | 26篇 |
1983年 | 21篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1974年 | 10篇 |
1973年 | 14篇 |
1972年 | 15篇 |
1969年 | 12篇 |
1967年 | 9篇 |
排序方式: 共有2237条查询结果,搜索用时 31 毫秒
1.
2.
Surface sediment samples taken by ? corer from 45 stations on the Norwegian continental margin and in the Norway Basin have been investigated for their benthic foraminiferal content. Unlike previous studies, the living benthic foraminiferal fauna was differentiated from empty tests comprising the foraminiferal death assemblage. Factor analysis of both the living and dead faunal data reveals six living species assemblages and five corresponding dead assemblages. The additional living assemblage is characterized by the arenaceous speciesCribrostomoides subglobosum that dominates between 1400 and 2000 m water depth, but is rare in the dead faunal data.Trifarina angulosa and, to a lesser extent,Cibicides lobatulus characterize the shallowest foraminiferal assemblage from 200 to 600 m water depth, where it is associated with strong bottom currents and warm, saline Atlantic water of the North Atlantic Drift. On the slope between 600 and 1200 m water depth, theMelonis zaandami Species Assemblage dominates, particularly in areas characterized today by rapid sedimentation of terrigeneous material. Between 1000 and 1400 m depth, where the slope is covered by fine grained, organic-rich, terrigeneous mud, the living foraminiferal assemblage is characterized byCassidulina teretis andPullenia bulloides. Below 1400 m, three foraminiferal assemblages are found:C. subglobosum is found from 1400 to 2000 m,Cibicidoides wuellerstorfi andEpistominella exigua predominantly live from 2000 to 3000 m water depth, and below 3000 m,Oridorsalis umbonatus andTriloculina frigida dominate the fauna.All of theElphidium excavatum tests found in this study and theCassidulina reniforme tests found above 500 m water depth were found to be reworked.Analysis of the sediment grain-size distribution and the organic carbon content in surface samples from the deepest stations suggest that the abundance ofC. wuellerstorfi andE. exigua is positively correlated to relatively coarse (caused by planktic foraminifera) and organic-rich sediments, whereas high frequencies ofO. umbonatus andT. frigida coincide with low organic carbon content. We suggest thatC. wuellerstorfi is adapted to deep-sea environments with relatively high food supply, tolerating relatively low interstitial water oxygen content, whereasO. umbonatus may tolerate lower food supply prefering well-oxygenated interstitial waters. 相似文献
3.
4.
Human placental alkaline RNAase inhibitor was purified to homogeneity. Activity was measured after each purification step. The final identification of the purified protein was done by two-dimensional polyacrylamide gel electrophoresis and by immunoblotting. Antibodies were prepared by immunization of rabbits with the highly purified inhibitor. The availability of the antiserum directed against the human inhibitor enabled the detection of RNAase inhibitor from various other organs and species. This procedure has the advantage over the usual activity test in that the inhibitor can be found even if its activity has been lost. 相似文献
5.
Prey capture rate (number of prey s−1 ) and the mode of feeding of Arctic charr Salvelinus alpinus were studied by performing foraging experiments with two sizes (1·1 and 1·8 mm) of Daphnia longispina prey. Arctic charr were particulate feeders at all densities tested. Adjusted for the effect of prey density, the capture rate showed a hump-shaped relationship with Arctic charr size for both sizes of D. longispina . Estimated attack rates ( a ) also tended to show a hump-shaped relationship with fish size. The estimated size-scaling exponent of the attack rate function, however, was relatively small, implying small changes in attack rate over fish sizes. Simultaneous estimations of a and handling time were used in combination with published data on fish metabolism and dry mass rations of prey to estimate maintenance resource density of prey as a function of Arctic charr mass. Maintenance resource densities increased monotonically with Arctic charr size, and rapidly as optimum fish size relative to attack rate on prey was passed. 相似文献
6.
The host specificity of Gyrodaclylus Solaris is examined experimentally with respect to its ability to infect the brook trout, Salvelinus fontinalis . The parasite readily attached to and reproduced on parr of this host and infections grew for c. 20 days from first monitoring (c. 30 days from first infection) before declining. Parasites could persist on this host for up to 70 days before finally disappearing. The pattern of infection resembled that seen in many other gyrodactylid species on their normal hosts, and suggested the action of a host response, In this respect infections of G. salaris on parr of S. fontinalis , anadromous Salvelinus alpinus, Oncorhynchus mykiss, Thymallus thymallus and Baltic Salmo salar follow a normal pattern, while infections of Norwegian S. salar are unusual in a continued unchecked growth, until the host dies, under pooled laboratory conditions. 相似文献
7.
Summary Albino mice were exposed to constant light for 7 days and were then transferred to periodic light. After initial photic damage and partial cell loss, the remaining visual cells recovered and survived as a stable population. Regions of the outer nuclear layer containing 4–6 rows of nuclei were more affected than those containing 6–10 rows. Changes in the synaptic structures in the receptor terminals of these two regions were recorded after varying survival periods. Some of the rod terminals had multiple synaptic ribbons and larger numbers of horizontal cell processes and bipolar cell dendrites. The number of terminals with multiple ribbons increased during recovery in periodic light. Morphometry demonstrated that the perimeters of horizontal and bipolar cell processes within the rod terminals were significantly larger than those in age-matched control mice, especially 4 weeks after recovery; they remained significantly larger than controls after 2 and 3 months. We suggest that partial loss of rod cells within a group of cells that are synaptically related to a common bipolar or horizontal cell results in synaptic growth inside the terminals of the surviving cells. 相似文献
8.
Ulrik Pedersen-Bjergaard Lars B geskov Nielsen Kai Jensen Lars Edvinsson Inger Jansen Jes Olesen 《Peptides》1989,10(6):1147-1152
Neurokinin A (NKA), substance P (SP) and the two peptides combined (SP + NKA) were injected intracutaneously on the forearm and into the temporal muscle of healthy volunteers. Pain intensity, cutaneous wheal and flare responses and tenderness of the temporal muscle were quantitated. SP but not NKA induced cutaneous pain. This relates the algesic effect of SP to the specific N-terminal amino acid sequence of the peptide, not shared by NKA. NKA, however, potentiated the algesic effect of SP as SP + NKA induced a significantly prolonged cutaneous pain sensation. Both peptides induced wheals, but only SP induced flare. These results confirm previous studies relating wheal formation to the identical C-terminal amino acid sequence of the two peptides and flare reaction to the N-terminal part of SP. Injections into the temporal muscle did not cause pain or tenderness. 相似文献
9.
J Thiele J Timmer B Jansen R Zankovich R Fischer 《Virchows Archiv. B, Cell pathology including molecular pathology》1990,59(3):125-131
In seven patients with chronic myeloid leukemia (CML) and ultrastructural and morphometric study was performed on neutrophilic granulopoiesis in bone marrow trephine biopsies. Bone marrow specimens from five patients without hematological abnormalities served as controls. In stable phases of CML, abnormalities of the maturing granulocytic lineage were most conspicuously expressed by an infrequently occurring nuclear disfiguration (blebs and disturbed bridging of segments). Morphometric evaluation included the numbers of azurphil (primary) and specific (secondary) granules, the cisternal length of the endoplasmic reticulum and the area of the mitochondrial profiles. These variables could be determined in early and late myeloblasts, promyelocytes, metamyelocytes, band cells and mature polymorphonuclear granulocytes. Statistical analysis with regard to control specimens demonstrated no significant differences in the total amount of neutrophil granules or of the other cell organelles. 相似文献
10.
C S Tannenbaum T J Koerner M M Jansen T A Hamilton 《Journal of immunology (Baltimore, Md. : 1950)》1988,140(10):3640-3645
A cDNA library from LPS-treated murine peritoneal macrophages has been screened by differential hybridization with radiolabeled cDNA from untreated and LPS-treated macrophages. Six clones hybridizing with mRNA sequences present in LPS-treated cells but not in controls were selected for further characterization. When the recombinant bacteriophage DNA from each clone was used as a probe in Northern analysis of total RNA from LPS-treated macrophages, inducible mRNA ranging from 1.45 to 6.4 kb were seen. In five of six cases, the mRNA expression was undetectable in untreated macrophage cultures. All but one clone identified mRNA that were inducible even in the presence of cycloheximide, indicating the independence of such gene expression from protein synthesis; none of the genes were superinduced by this treatment. The time course of expression differed among the individual genes. Four were induced transiently, whereas two showed stable increasing accumulation through an 8-h period after stimulation. In addition, four of the genes were seen within 30 min of stimulation, whereas two were seen only after 2 to 4 h. Two genes were induced only by treatment with LPS, whereas four were also induced in response to other agents, including IFN-gamma, macrophage CSF, and PMA. The insert sequences from these recombinant clones did not hybridize with a set of cDNA encoding other inducible gene products, including TNF, IL-1, ornithine decarboxylase, c-myc, c-fos, JE, or KC. Thus, these six cDNA appear to encode inducible macrophage genes that are distinct from one another as well as from a selection of previously described early genes. Although their functional identity remains indeterminate, they may encode previously described early proteins induced in macrophages treated with LPS. 相似文献